My powdercoater powdercoated my frame, spindles, brake rotors, calipers, exhaust manifolds, and a bunch of other parts. He said that to powdercoat a rearend that I would have to remove all the gears, seals, and fluid. They first sandblast all the metal to make a good surface for the powder to bond to so they need everything removed and cleaned. As far as powdercoating over the filler, my powdercoater said that only certain fillers can withstand the heat from the oven but if that's the case, he can't guarantee the part since the powder maynot bond to the filler properly. You might wanna check out
www.airborncoatings.com or my powdercoater at
www.centralctcoatings.com You can probably throw them a call and ask them yourself if you have any other questions.