just noticed that Motobins are doing new driveshafts, both 16 spline and 20 splines at a real good price. if you are looking for a new one then definitely check them out. Priced at 95 pounds, hard to get a good S/H one for that.

good news!!!

Bit the bullet and ordered a new one last week. It arrived today

This seems to be an original shaft and the price is very good.
Is it a brand new one or a reconditioned one?
Motobin is selling the splines and may recondition their shafts.

Brand new, motobins are no longer reconditioning shafts, they still sell the splines, I have another shaft at the engineers now getting a new spline welded on, but they no longer supply exchange shafts like they used too.

Checked their website, price seems to be for 20 spline only.

Yes, I saw that, my first post was incorrect, it is only the 20 spline ones at a good price.

OK I fitted the new driveshaft today. There must have been a modification to the specs of the drive shafts some time in the past. The new drive shaft is actually larger at the universal joint end and will not slip up the end of the swing arm. The opening in the end of the swing arm is 55mm and the diameter of the drive shaft universal flange is 55.25mm. A few minutes work with a coarse file on the swing arm and it fits. If you look at the photo above you can see where the driveshaft steps up in diameter by the UJ, the original one does not. But it is not a big job to open up the end of the swing arm .25mm (only in 4 places required)

After fitting driveshaft in said manner I emailed Motobins about it, I also mentioned that the spline was as not as tight fitting as the replacement spline I got at the same time. This is their reply.
Sorry this is a genuine BMW item and this is just how they come now to fit
them you need to remove the swing arm and drop them in from the gearbox end.

As for the spline not being as tight as the replacement spline this is
because we have the replacement splines made very slightly oversize as they
are usually being fitted to final drives that have a very small amount of
wear.

Regards from Damien

Moto-Bins Online

Due to the fact that the repair spline is slightly oversize (undersize) I would suggest that it would be a better option than a new driveshaft, unless the spline on the final drive is 100%. .
Robin