Lucas Oil
I have not heard anything bad about them, but you may also want to look into Marvel Mystery Oil.
Supposedly, Lucas makes several blends for different uses (engine, transmission, fuel tank, etc.).....but the Marvel is a "one type for all purposes" kind of product.
I have used Marvel in the crankcase and fuel tank of a commercial-grade diesel truck, and never had any problems. Then again, perhaps I would have not had any problems if I had not used it either.
:beer: