If they are all rusted and thinned out the screw will not work. Punching it into the coolant jacket has been done by just about everyone for many years. I've never heard of any ill effects.
When punching on one side or the other many times the thing will turn sideways in the hole and that enables pulling out with pliers.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

professional bovine relocation specialist