'Medicinal' castor is TOO filtered to lubricate properly. There is NOTHING wrong with using 'Baker's AA' castor for the 'first few runs' in order to break in any glow engine. Most engine manufacturers advise to switch to/use a 50/50 castor/synth mix, or less castor, for use after break-in.

It's YOUR engine, treat it how you want to...it will either last practically forever or FAIL prematurely...depending on how you 'run' it.