I have found if you use Byron's Race Premium R/C Car Fuel you do not need to use an after run oil. All you need to do is drain your tank at the end of the day and run the engine at idle to burn all the residual fuel out of the engine and fuel lines (try re-starting engine several times just to make sure).

With other fuels it is a good idea to use some after run oil. First let the tank run completely empty at idle until it runs out of fuel (try re-starting it several times). Next put a few drops down the carb (make sure area around carb is clean) and a few drops down the glow Plug hole (leave the plug out and put a rag over the top of the engine) and spin it over for 5 seconds on the starter box. Last put a few more drops down the carb, reinstall the glow pug and spin the engine over 5 more seconds.

If you do not have a good after run oil other substitutes would be automatic Trans fluid, 3 in 1 oil or Caster oil from the drug store!