2000 M900 exhaust header stuck, help?

[papadacus]

2000 m900
one of the two nuts that clamps the header to the cylinder head (the lower front cylinder) is rusted stuck and too corroded to fit a socket around. I gave vice grips a shot and have soaked it with two types of penetrating fluids but i ended up stripping it worse. Any suggestions for removing it?

[Ddan]

Heat. 

[dlearl476]

Heat, lots do penetrating oil (I prefer PBlaster) and tap it lightly with a hammer in the direction of the stud a few times. (LIGHTLY!)
Get the penetrating oil up into the head, too. With any luck you can get the whole thing (nut and stud) out of the head without an thread damage to the aluminum head.
Then just replace the stud and bolt. (And use anti-seize goo)

[Ddan]

If you do apply heat to the cylinder use a little care as the aluminum won't turn red before it melts.  You can use quite a bit of heat just keep the source moving a little.