I'm gonna guess that you didn't have the transmission end fully in. I've never removed that end and the rear alway went on with a few minutes of fiddling.Many of those videos are very helpful - HOWEVER - I have just finished lubing the splines on my 2016 GSA and it was a total disaster of an exercise!!! I pulled the entire driveshaft out, cleaned everything up and lubed everything and then went to reassemble everything. I had little trouble inserting the driveshaft on to the gearbox end BUT the final drive end took me the better part of 2 days of trying and retrying before it managed to pop on!!!!!! I actually ended up inventing new swear words! It just seems to be the luck of the draw - when it eventually popped on it was totally without any pressure or resistence. So - be warned and be patient!