Updated or did they finally figure out there was no need for two drive shafts in stock. Sure the touring had a larger diameter spline going into the final drive but the rest of the shaft was identical. I am not sure if the Roadster just switched to the same drive shaft for ease of parts stocking or if it is stronger. Sure as long as the tooth size has not changed and the diameter expanded would seem to be stronger but if the spline cup on the final drive unit only had the internal changes and the Outside diameter of the cup remained the same I would say it then got weaker. So go figure. If I had one I would be measuring the spline and cups to see but alas I have not had the need for Roadster or Touring parts
Oh then other then the older ones needing better grease from the factory (which they have changed) I do not remember anyone breaking a drive shaft or the spline cup on the drive unit. Many of us were above 200 hp and massive torque before the touring came out without destroying the final drive units.
Now that being said have you pulled the unit yet?
If you did is there signs of oil migrating up into the swing arm?
If so I would suspect you lost the seal and of course you know where the oil went.
If not then I would have to ask who did the last lube change on the final drive?
I would definitely look so you can figure out whether the drive shaft spline is toast also.
Anyway just thinking out loud here