Spline failures don't happen to every r1150x. There seems to be a misalignment either with the transmission case or somewhere in the clutch assy. A reputable BMW wrench in my area recommends replacing all the clutch components as you did. I was planning on taking a look at the splines this winter with the assumption I could make it 30k. Instead, they failed when I was 600+ miles from home. It might be a good idea to take a look at yours in the off-season.
Here's my first input shaft:
Looks a lot better than my current one, but the first one was found prior to complete failure.
I was thinking about my options with this bike. I'm going to fix it and trade it in on something. The next question is what to get? It's got to have 3 locking hard cases and be comfortable enough for all day rides (more comfortable the r1150r would be nice) Here's the short list so far...
Kawi Concours - decent price and fast. Comfort is a ?? Hard to find one to test drive. Could be like a ST1300.
Ducati Multistrada 1200 - pricey sexy fast. Chain drive though.
ST1300 - looks good on paper, but boring boring boring to ride. Not really on the list.
R1200RT - pricey but otherwise OK. Downer - made by the same company who's name I'm cursing now.
R1200R - decent price, lightweight and I would probably love it. Downer - see R1200RT.
HD Electra Glide Ultra Limited - comfortable for rider and passenger, plenty of dealers around that are open on Sundays and Mondays, good resale value, sound system, ride-by-wire, cruise, ABS, etc... BUT - PRICEY , 900 lbs and would require me to rip the sleaves off my shirts, get tattoos and grow facial hair etc..