The guy in the hobby shop is going to try to SELL YOU SOMETHING. The 20% nitro costs more and he gets rid of it. If it tears up your engine, he can sell you a new engine?

I doubt if he's ever used a bushing engine? Or even knows which ones have bushings and which ones have ball bearings? Or knows that they need more oil in the fuel?

Back in the "old days" almost all model engines had bronze main bearings and also had cast iron pistons. Fox Super Fuel was 5% nitro and 25% oil back then.

Don't use Cool Power in a Thunder Tiger GP series engine. I don't use it in anything. I like the fuels with a blend of castor and synthetic oils for everything. However, I do not own any plain bearing engines anymore.

However, you can put caster oil in Cool Power fuel.

You can buy castor oil (Usually the Sig brand) in quart bottles at the better hobby shops. You can also buy Morgan's Cool power oil and Omega oils. There is also the Klotz brand of oil. You can also go to the discount store and buy castor oil in little 2 oz and 4 oz bottles but it usually costs you more money than the hobby shop kind unless the hobby shop is trying to charge you too much.