Fried exhaust cam/bearing caps sure sounds like oil starvation, or poor oil quality. Yeah if the bike runs lean it'll run hot, but if yer using good oil and keeping it topped up it won't fry the cam...but low oil level will--quick, fast, and in a hurry. If you were running lean enough to experience engine failure, you'd likely have a hole in the piston. And as for the retarded design, lotsa Jap bikes don't use replaceable cam bearings, and still somehow manage to be reliable and long-lasting. Like Honda's air-cooled XR/XLs for example. Ya gotta keep oil in 'em though.