well, ever since I switched to Castrol Syntec on my 2000 VW, I've been changing every 10k miles. I'd be willing to be that I'll never have a premature engine failure for worn rings, bearings, etc.... On the Bonnie, I do it every 6,000, but only because I'm a little leery of the fact that our motors have the crank and cam riding directly on aluminum journals, not on bearings (unlike my cars), and the fact that the bike is air cooled. I plan on handing over my '06 Passat to my son in a few years, so it should hit 200k within 5 or so years. It won't be the engine that finally makes us trade it in though, even with the turbo, but rather the nickel and dime stuff like electricals, emissions, etc....
