The clutch is not subject to the high heat of brakes. That lets BMW use mineral oil instead of brake fluid in the clutch circuit. I don't know what BMW uses today, but when the R1200 first came out they were using a BMW branded version of Magura Blue Blood.
But before you worry about the kind of clutch fluid, have you checked the clutch fluid level? I can not say this often enough given how many people don't understand: as the clutch wears the fluid in the reservoir rises. If you don't open the reservoir every once in a while (I check every service) and make sure the fluid level is not above the MAX indicator you can run into the situation where the clutch never fully disengages which leads to slipping.
That's a good point, Marc. I've wondered before why there isn't a service point in the manual about checking the clutch fluid in the reservoir. I never stopped to think that it might get too high. I shall check mine at next service.