Honestly it's insane with the prices people ask for. Thag would be your best bet. Would be pick up a roller or slider. And throw a brand new "ENGINE". Electric RC's have motors. Nitros have ENGINES. Yes there is a difference..
"ENGINES" run on fuel nitro gas methanol
"MOTOR" run on battery...
I agree 100% with @cbaker65 . First thing is break down the engine 100%. Rite down to the crank shaft. Check inside and out and the carb. I personally have never used any sort of after run oil. And I've never had any issues with my nitros. I also turn then over every couple weeks keeps things...