Ok. So IF I decide to whack it.....(clears throat) I mean. TAP it with a rubber mallet that I don't have; and I manage to get it loose. What EXACTLY will be required to get it to re-seal?Tap the cylinder with a rubber mallet. TAP, not whack. Do keep a couple screws in the flange about 1/3 to 1/2 way in.
Alternate, put the engine in the over at 250* for about 10 minutes. use gloves when you take it out. Sounds like someone might have used something on the flanges as a sealant.