I dont think you would want to do that. Putting oil or anything onto the metal after its cleaned would interfere with the weld (at least that is how I see it) I may be wrong. I would go with whatever motorgeek (aka Jerry) says.

After its cleaned you can always drain and fill the case to remove as much small pieces of the aluminum as possible. but then again the small bits of aluminum probably would not do much if any harm to the steel gearing inside of the motor, better to not risk it though.