I'm bumping this old thread, since I've seen something similar, which may or may not be useful to someone.
Seven years ago I got myself new valves for my then new-to-me R80/7, primarily for peace of mind (dropped valve syndrome) since I got no info on previous head work on the then 70 kMi bike.
Bought new BMW "original" valves myself, but ended up sending the heads to one of the most recommended independent BMW boxer experts, to get the guides replaced.
Since then, on a few occasions when setting the valve-rocker gaps, I noticed closing up gaps. Despite use of lead replacement additives, I thought the heads were suffering from valve seat recession, and prepared myself for getting unleaded seats fitted.
When I recently took off and dismantled the heads, I couldn't get the exhaust valves to slide out. It turned out the cotter grooves had mushroomed:
= RIGHT valve stem
= LEFT valve stem
The seats were fine, indicating that the closing up gaps I had noticed were stretching of the tip of the valve stems.
As opposed to the valves Rob Farmer posted about, the top of my exhaust valves wasn't damaged to the extent that the manufacturer's markings wasn't visible: they were AE valves.
So either I got sent the wrong valves from my supplier (I found the receipt, which clearly specifies the "BMW original" valves, both in terms of part no. and price), or the independent expert who did the head work (the invoice states "labour to cut seat and lap: 4") had them mixed up.
I've since then had a few pairs of Intervalve exhaust valves fitted, but so far without sufficient mileage on them to be able to check for stem/cotter groove damage. Hopefully they are OK. Considering the time of purchase, my new valves & the ones reported on by Rob also in 2010, it could be a bad batch from AE? In any case, I'll double check that the "original BMW" valves I will replace the AE ones with indeed are TRW ones!