Other then Traxxas no engine manufacture recommends WD 40! WD 40 displaces moister where after run oil adsorbs it. To me for no more the after run oil cost it is just cheap insurance to use the proper oil! Call or email HPI and see what they say. You all so need air filter oil. Keeping the air filter clean and oiled has a lot to do with how long your engine last and how it runs.