A small pipe wrench can work better than vice grips for getting a grip on a stud that is being difficult. (A lot of my wrenching experience is on cars far older than the ones we are discussing here, so dealing with corrosion and stuck fasteners is a way of life.)
Also, not to restart a flame war that's been going on for decades, but WD-40 is not a penetrating oil. Use a real penetrating oil like Kroil, Liquid Wrench, or PB Blaster. Or if ou have some acetone laying around mix it 50/50 with ATF and put it in a hand oiler and use that, it works surprisingly well.