My understanding is that a high quality synthetic such as Amsoil will leave fewer deposits than a conventional or low quality oil. However, it seems to me that if you're having "coking" of the turbocharger, possibly letting it cool before stopping the engine would have a more dramatic effect than using differenct oils. The factory turbo's on our engines seem to be pretty tough. I don't know of anyone who's blown one up or worn one out. I'm sure it's been done, just not by anyone I know.