This is my 2nd bus and the 2nd top end tune up. On both buses I have had to replace 3 roller rockers due to what looks like the surface starting to fail. On this bus one of the cam lopes also started to fail. So in my opinion the top end should be looked at somewhere between 100,000 to 120,000 miles. It would have been a lot less $ if I didn't need to replace the cam.
Ray Davis is kind enough to post these pictures.