Purchase the new cap before, you'll see it's internal configuration. There is a rubber seal under, the ideal would be to not cut through it, preventing cut disc and plastic particle in the brake fluid.

 

I’m confused why you’d have to cut the cap. The threads do have some notches but should be able to overcome the tabs. I’d look for a way to secure the reservoir (to not break it) and get some type of channel locks or strap type filter wrench to remove it.

 

Put a dress shoestring or thing string around the cap where it meets the reservoir and pull tight to depress the locking tabs then unscrew. Pliers, pipe wrenched or cutting wheels are not to be used unless you want to render the cap unusable

 

I do plan to buy the cap items before going ahead with the surgery; hopefully the rubber boot keeps debris out of the reservoir well. I did think about forcing the cap over the locking spring fingers, however I'm nervous about cracking the tiny T10 thread bores that hold the reservoir to the assembly. If I didn't hold it perfectly still while forcing the cap off I'd be putting a lot of stress on the plastic threads.
PerazziMX14, I've tried the string method and the removal tool with no success which is why I have this issue. I believe the spring fingers have some how bent and no longer move. BTW, was easily able to remove the clutch reservoir cap which has a smaller version of spring finger insert with the string method.

 

Moto tool and carbide dental burr will allow you to slowly eat away the plastic where the spring clips are and see what is happening before you do anything major. Once you expose down to the metal you can probably push in the spring fingers with a small screwdriver and unscrew the cap.

 

The fingers may have been distorted from someone trying to force the cap on off. I'd not give up on the string method just yet. Tie the string in loop and then insert a screwdriver and twist the string like a tourniquet to get some additional pressure on the fingers and hopefully squeezing them inward enough to get the cap to spin free. For the record you are not trying to see how much pressure the reservoir can take before it implodes you are just trying to flex the fingers back.


The clips are plastic, not metal

 

Thanks for the tip CallMeSnake! Found this in my bag of dremel attachments. I like the idea of going "minimally invasive" to avoid damaging the reservoir. If I just make vertical cuts inside the reservoir slots, I may get lucky and be able to carve out or extract the retaining fingers. Then as you said, unscrew the cap.

 

Problem solved, but don't exactly know root cause.
Took a closer look this afternoon and observed the spring fingers don't flex like the ones on the clutch fluid reservoir. Being flush to the outside wall of the reservoir, no amount of string pressure inward was going to have any effect. This gave me the idea that the fingers might be disengaged from the cap serrations and the courage to try a filter strap wrench as Krons suggested. After squirting a bit of silicone lube under the cap into the finger slots, the cap twisted off after a couple of trial and error attempts with strap wrench positioning. You can see the locking fingter insert and reservoir look okay except that for some reason, the fingers have flexed inward enough to disengage from the serrations and taken a permanent set (maybe heat related?).
I'm happy to say, I put away the dremel without having to use it and can now get to a long overdue brake bleed.
Thank you all for sharing your insights!

 

Plasticrap at its finest. Living in a heat zone I find plastic rot happens on all types of objects. Looks like you got lucky & didn't have to destroy anything, this time.

 

Ah but the finger do flex inward to disengage from the cap. When you slide the plastic cage over the reservoir it spring the tabs outwards but the beveled teeth on the cap allow the tits on the the tabs to be pushed inwards and pass by. Loosening is altogether as the teeth on the cap are squared off and will not allow the tabs to pass unless they are flexed inwards a teeny tiny amount.

The string is still a good thing to use, believe it or not.

 

I'm tempted to just cut those side wings off. Don't see what actual purpose they serve. Not like there is a rash of people messing with motorcycle resevoirs. Maybe to keep the cap from backing off under vibration? Or a regulation requiring secondary locking system. All my newer vehicles with plastic caps have some sort of secondary lock on them, but nothing as stupid as this.

 

I'm tempted to just cut those side wings off. Don't see what actual purpose they serve.

I think the tabs are more to properly locate and help seal the rubber piece without spinning as it is tightened. If that plastic spins the rubber could crease/bunch up and not seal.

I suspect the OPs cap was over tightened, but that plastic appears to potentially be deformed making the removal more difficult.

 

Looking at the pictures, I think you could cut the tabs off but leave short stubs to prevent rotation while disabling the locking feature.

Agree that the OPs issue was probably overtightening or attempts to remove with too much force at a previous time. Either one could have twisted the plastic tangs and if left in that state for long they would take a set, making it difficult or impossible to press them in enough to get past them.

 

It makes sense the locking finger insert serves the purpose of allowing the cap to seal the reservoir rubber bellows without distortion as its rotated on and maybe satisfies a "secured cap" requirement as well. I so wish they had just used a couple of screws to hold the cap on like most other bikes.
In my case, the fingers were not twisted, but lost their outward flair maybe because they were forced inward by the cap serrations while tightening and left in that positon for a long time. The cap serrations have a ramp on one side that allows them to flex inward while turning CW and a more vertical wall on the other to lock the fingers in the CCW drection.
I'll leave them as is because I don't think the cap is going to undo itself since compression of the rubber bellows flange acts like a split lock washer, keeping a bit of tension on the cap threads.
Now that I know what's going on, I kind of like being able to just twist the cap off without messing with the fingers.
You could cut off the fingers just below the flange to remove the thick part that engages the serrations or as The Old Mechanic mentioned in one of his videos, grind off the portion of the finger that slots into the serrations.

 

Leave the tabs in place, don't overtighten the cap and future cap removal will not be an issue. I have never needed more than a string and a gentle twist to remove the cap.

 

Dental floss or a skinny shoestring (I use two around my tool roll so I always have these with me) works for me.

 

I must be doing something wrong, I don’t even push the tabs in when I unscrew it every two years or so.
🤷‍♂️

 

Well Krons, check the way the locking finger insert sits inside with the cap removed. Sounds like your's might have the same condition as mine in the photo above. I presume, the design intent was for them to rest in the cap serrations with a small amount of spring force.

 

If you do not tighten down with herculean force it will still seal but the finger do not fully engage. What Krons has experienced is also typical of what I have. After initially removing the cap using a string most subsequent removals have required nothing more than turning the cap counter clockwise.