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I have used some stuff called Hancolite to remove gaskets. MEAN stuff. It has toulene (sp???) and some other 'lenes' in it.
It will eat a gasket in seconds. Gaskets turn into mush, literally.
(It will take paint off of a car in a matter of seconds, too.) Paint becomes a mass of crinkled crud. Flakes right off. Down to bare metal.
Stuff is hazardous. Can't get it anymore.
You can buy straight tolulene from Sherwin Williams. It is used as a paint thinner to give a pearl look.
Prevention is best of course. In the days before there were hundreds of gasket sealers on the market, mechanics used to coat paper type gaskets with light grease and let it soak in before installation. This caused the gasket to swell slightly so that it would conform to any irregularities in the mating surfaces. The grease also preserves the gasket so that is lasts longer and if you have to take it apart it never sticks.
Don't use a wire wheel if the engine is in the vehicle, at the dealership we had a rash of problems with pieces of wire getting into the oil pan through the valley and getting sucked up into the oil pump causing a seizure. Of course this was in the days when you did a valve job not just replacing the heads...
Knotted wire bell brushes in a die grinder are hard to beat on any surface. It will eat aluminum if you dwell to long, but makes short work of ever the almost imposible to remove print o seal gaskets that HD uses as cylinder base gaskets.