Hey guys. I'm running a os .40 fx and I had a few quick questions. I get some brown residue in the muffler and in the engine itself when I remove the back plate. It runs fine but I was just wondering what you guys think it might be. I don't think it's rust as I can see anything that looks like it's rusting.

The other question I had was about after run oil. What is that all about. I'm running 10% nitro fuel and I'm not sure of the oil content because I'm work. SHould I be using something different or something extra?

Thanx
Luc