[69BBsuburban]

If you have an older engine....it's best to NOT use additional oil additives, as they tend to clean the sludge from inside the engine and then it'll start leaking....some of the "cleaners" that you slowly pour down the carb do work, like the GM stuff you get at the dealer.
And if ya gotta add an additive to an AT trans, "rebuild in a can", you've got problems...

The only oils used in all my cars are 20w-50 oil, Dextron III ATF, and 75wt-90....oh, and D.O.T. III.....