Hi There 1QwkSport2.5r
Using straight Castor Oil definately needs after run oil, specially before storing your engine.
The best to use is Auto transmission fluid. This completely dissipates the castor oil and the nitro leaving your engine nice and free till you use it next.
If you don't use these steps you run the risk of damaging your engine internally as nitro residue is corrosive and the castor will dry and gunk up your bearings etc making it very difficult to clean out.
Any other suggestions?