Use a Propane torch to warm up the flange and soften whatever gasket glue was used the last time the pan was installed. Obviously, clean off as much accumulated oil and grease as possible before applying heat. If you're the type of timid stovebolter who wears lace on his drawers and gets a case of the vapors at even the mention of a flame, use a heavy duty heat gun instead of a torch! I keep an air hose and a blow gun handy to blow out the fire in case I get a little over-zealous with the heat.

PSA: Saying "Bel Air" on a truck forum will get your knuckles rapped with a big crescent wrench by one of the moderators!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!