Just been doing a sludge patrol on the tin-top sump (where does all that cr*p come from?).
Inside was pretty glazed with dead oil etc.
Needed something rather than elbow grease to shift it - out came the NitroMors paint stripper.
What would have been hours of work was shifted in about 10mins. Probably best to be cautious though as I would assume ali. doesn't like being exposed to that kind of solution (although it does say "Kind to metal" on the tin).
Cheers, Pewe

i used paraffin. Worked well too.

as long residue doesn't come off into the oil, and stop it coating engine parts properly (just a thought)