Im also rebuilding a dt175mx, i have just got the frame, swinging arm and lots of smaller parts back from the powder coaters all in gleaming black, the parts i sent were very rusty, all i did was degrease & power wash the parts, as oil will affect the quality of finish, even though the coaters will blast off all traces of rust & old paint, also if you are interested in doing this for your own project a good tip is to fill any threaded holes in the frame with old bolts, which protects the threads and makes things a lot easier when you come to building it back up . best 80 quid youll ever spent......... cheers 3dtees.