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I sprayed a bunch of PB blaster on it for about a day and a half. When it came time to take it off, I heated the bung with a torch and then sprayed compressed air on it...
I repeated this about a hand full of time and it came off!
BTW, use a 6-point 1 1/8" socket. The 12-point's notches are too fine to fit around the somewhat rounded drain/fill plugs.