Core plug seized

Any one got any tips on how to remove a very seized threaded core plug from the block of a series 3?

regards
Pat.
:doh:

there is a spray you can get that freezes the seized threads and breaks the bond. i have only seen it at one place and when i asked the guy about it he says it is very good stuff and works well on seized nuts ect. i think it is like a liquid nitrogen and contracts the the metal breaking the bond. the other method is to heat it up or drill it out then use heat and a square bar hammerd into it and try to turn it out that way or just drill it out close to the size of the hole and rethread it.