Good advice above- I think the clutch is the culprit. Either while waiting for the parts, or soon afterwards, I would drain and refill the final drive and "lube the splines." This is unrelated, but since it doesn't appear to have been done before you should do so at some point. That will put your mind at ease about the final drive and/or drive shaft. I've had two go out on my Roadster (which is very unusual), even with regular service, and you don't want to go through that $$$.