I'm just curious: how much mechanical imperfections in engines do you tolerate? I'm in the process of reviving a late-90's era Athearn SD40-2. What I can do with it is make 4 of the 6 axles work, and use a motor that's not in perfect condition. I can't buy axle gears and a new motor right now. There's no local hobby shop in my city. Mike B.