ORIGINAL: jaka
Hi!
Run dry doesn't mean everything is fine inside the engine,there is still some fuel residue left.
Over here in Europe where all synthetic oils are dominant since 15-20 years ago we have no problem with rust due to the fact our oils (Aerosynt 2 and 3 and Motul ''Micro''!) contain rust inhibitors.
We just run our engines and store them...that's it!
I would guess that you don't burn much nitro either. Either way, some castor provides a good bit more protection against lean/hot runs and rust.