The issue with BMW drive shafts has always been the u-joint. U-joints can only tolerate a slight mis-alignment before they begin binding at that point of rotation.
Remember hiking up the rear end of your 60's muscle car? Or lifting your 1/2-ton 4x4? and the increased consumption of u-joints?
One can Google the joint and go learn more about it.
The GS with it's increased ground clearance makes a mess of this. They seem to last about 50,000 miles which is around where we used to see /5 and /6 BMW bikes begin to show drive shaft problems back in the day.
Over the years I've replaced the drive shaft in my first BMW, a 1974 R90/6, my last airhead that had a 1984 R80 RT running gear and 1982 R100RS motor. And now twice on this thing.
Chains and sprockets were replaced on my old Fireblade at about 30,000 mile intervals when I used good ones. I think I used to run a 530 chain. I wasn't concerned with racing weight I was concerned with commuting. No one was paying me to wear out their chains and sprockets, so big and tough were the orders.
I think the weaklink in the BMW design is the assumption that a $800 wear-item sub assembly is OK. Personally I think it's bullshit. Adding more horsepower and torque to the equation hasn't helped any.
I'm working my way toward 200,000 miles in what will be something like 9 years, thanks to way too damned much work travel. Without the travel I'd have whistled past that mile marker a couple of years ago.
"You don't go to Mongolia for the food."
- Sebastian & Kim
2010 KTM 990 Adventure R
My Life With The 990R