How to remove Exhaust Manifold Elbow from Manifold

[FishermanDave]

Hey all! I'm trying to take my exhaust manifold elbow off my exhaust manifold so I can replace the gaskett. The only problem is they are stuck together. I'm not sure if it is from rust or there was a leak before (which caused the rust) and so they were stuck together with some "supper substance" that doesn't come appart. Anyway, any reconmindations on what to do. Thanks for any help!