A seized hand hole gasket ate up most of my Friday in Gary

Had to pull a hand hole cover on a 60 inch drum at a mill in Gary last Friday and the gasket was baked on solid. I figured it would be a 20 minute job so I told the foreman I'd be back by lunch. Two hours later I'm still chipping at it with a putty knife and a wire brush, afraid to get too rough with the seat. What finally worked was soaking the seam in penetrating oil and letting it sit a full 15 minutes while I took a coffee break, then it popped with barely any force. The old timer I work with says he does that every single time now because rushing it is how you gouge the seat. Anybody got a better trick for stubborn gaskets on the water side, or is the soak and wait just the way it goes?