I stopped using castor in the very early eighties because of the mess it made of my models and have never even considered going back. I have never in all that time had an engine wear out or falter in any way. For 99% of engines castor belongs in the stone-age.
For me the horrible job of removing the mess from my models after a flying session was enough to put me off for life. The one exception being the Moki 210 in my Extra 300s. Just M.O.H.O.