[Alan Roehrich]

Oven cleaner will remove most of it, given enough time to soak, and if it is kept warm. Then wash it at the car wash if you don't have a high pressure washer.

Often you'll need to soak them for a while, and it helps a lot to knock off all the heavy, thick, loose stuff, before you try the oven cleaner. The "purple power" stuff works well, as does "Simple Green", used in high concentrations (at least 50/50) after the oven cleaner has been used.

If you use "caustic soda", like you'd see in a machine shop for cleaning cast iron, the aluminum case will contaminate the solution, and make it foam. It will also make the case turn dark. The case can be brightened up with etching mag wheel cleaner, AKA phosphoric acid.

As to what transmission shops use, most use a high pressure spray cabinet, with the solution about 180 to 200 degrees, and one of the best soaps is Safety Klean floor soap (the 666 stuff).