of its a regular small bolt in the gib holding the knives in then an impact driver is useless it doesnt access the bolt from the end to get a socket over the head. Recently had a stuck bolt on my alternator bracket and could not loosen it to put new bearings in. Heated it with propane torch yellow cylinder not tons then misted water on to whatever level I wanted with those simple water spray bottles. Did that several times and it was enough after several times to make it break free. Those bolts are not the best size wise and you dont always have excellent access. Sounds like it was well overtightened unless it got rusted in place