I had my valves and seats replaced 9 years ago. I have the dreaded '81 model year that was prone to valve face plastic deformation, a technical term for rapid valve face wear. It started out as a timing chain replacement, progressed into exhaust thread repair, and when I got the heads off and looked at the exhaust valves, about 80 % of the valve face was worn away. The shop that did the overhaul was San Jose BMW, and they said that at best I had 5,000 miles before the exhaust valves would have failed. I guess it's one of those areas that needs investigating if you have a high mileage R65.