I finally had some time to remove and inspect the final drive and driveshaft:

The good - all diff gears and bearings are in excellent shape with no excessive movement, no damage or wear at all to the gears and it rolls smoothly.  The input end of the driveshaft does not have any wear and there was some white grease still evident in the splines.

The bad - BUGGER! The output of the drive shaft is worn as are the final drive splines, quite badly.  There is no sign of fresh lube and what was there was dry, red gunk that had to be scribed out.

Having read through posts on the forum I have come to the conclusion that the bike is still okay to ride gently but I will have to start to think about saving and fixing my worn rear end (!).

Is there a "Brunos" in Australia, or anyone who fixes or replaces worn splines?

might still be ok on the output shaft for a while grant ......don't have a solution for the bevel box pinion though .....
many of the locals have exchanged the bevel box and drive shaft  for something a little less worn

just a note of caution ...the early series up to mid 85 had a bevel box with 16 tooth splines afterwards were 20 tooth ...so be aware of what you are buying to suit what .....(the output shaft on all is still 20 tooth though )  for what its worth ...hope it helps

good luck mate !

If I can figure out how to (must be missing something somewhere) I will post some photos of the final drive splines.

Check this guy out he is a bit pricey but has a good reputation. http://www.bombarsbeemers.com/Pages/BMWComponentRepair.aspx

grantf2 wrote:If I can figure out how to (must be missing something somewhere) I will post some photos of the final drive splines.

Give this a go, and there are several other posts about too:

https://www.k100-forum.com/t4267-posting-a-photo-update

It's easier than it seems at first. Good luck.