Right around 60,000 on my '99. All the normal fuel pump issues, CCT recalls whatever. It's been pretty rock solid with decent maintenance. Finally decided to check the valves a couple weeks ago. Never had the cam cover off before then. They were all still way within spec. Talked to a Busa mechanic I know and he said it's really rare for them to be out of spec until at least 85,000 miles. I wonder why they want you to check 'em every 15K?
Gar