[Pete Munroe]

Doesn't seem possible to use a "impact driver" on a shifter stub sticking up on an installed trans...you better have a "dolly". or bucking block to match the blows you are putting on the assembly or there is not going to be any impact to break anything free.

Heat seems better. A machinist friend of mine uses a torch to heat the head of a rusted/locktited bolt...he heats it red, briefly, and then gives it a whack with a hammer. But, those parts are solid mounted...not floating in the breeze like a shifter stub. In this case it was brake calipers on a older 911 Porsce

A impact hammer on a unsupported bolt isn't going to do much but break/bend the part part you are beating on.

All that said, I have been rather disappointed to see any bolt ever installed by me with red or blue, to be easily removed, more or less. I thought I was good at removing any lubricants from the threads, or, maybe my red-locktite is out of date.