As @snottyotter says
Vice, clamp hell out of, heat moderately, apply good penetrating oil (Kroil is my best friend in a workshop), tap with deadblow hammer or punch back of threads. Repeat, over a week if necessary.
Have found the usual, heat, kroil, whack and repeat over a long period of time but without going crazy on the force yields best results.
WD40 etc is a waste of space, almost a useless product IMO.
As @snottyotter says
Vice, clamp hell out of, heat moderately, apply good penetrating oil (Kroil is my best friend in a workshop), tap with deadblow hammer or punch back of threads. Repeat, over a week if necessary.
Have found the usual, heat, kroil, whack and repeat over a long period of time but without going crazy on the force yields best results.
WD40 etc is a waste of space, almost a useless product IMO.