Hey, man's gotta have a hobby...
Ok, not budging today either despite plenty of PG and brute force. I shall try heating and a 50:50 mix of acetone and ATF as a penetrating fluid- supposedly the best thing this side of my bottles of noxious acids, and far less likely to damage the paintwork or me...
Any more news Pedro? I'm convinced it is the bolt corroding in the engine block which means about 8-10" or so of corrosion. Not likely to be beaten easily.