I have recently been working on a recently acquired K75 which had some clutch issues. During the tear down, I found the splines in the drive shaft were worn. 21k miles on bike. All being taken care of once the brown truck arrives.
Progress forward to today. There is an '85 K100 with 30k miles for sale. Pictures make it appear to have the FYK. Asking a little more than willing to pay, but it is negotiable. In talking with the owner today provided an offer that he seemed to be amenable to. Will offer $800 as is. If I have an opportunity to pop off the rear wheel and final drive to inspect the splines, I will adjust my offer accordingly. If the splines are worn, $300. If the splines are in good shape, $1200.
We will know Sunday if he accepts.