Servo clevis seized??

Having gone through the ordeal of removing the servo from car and getting hold of a 16v servo without having my pants pulled down over price, how do I now get the clevis off the rear of the servo?

Both seem to be completed seized solid and I've already snapped a couple of spanners trying to unscrew them

Any ideas or tips before I give in and let an engineering firm get them undone? 

Yeah, ive removed these before no problem, but my latest just will not undo and I don't want to break anything. maybe some heat..