Air chisel. Most locks that are worth a darn are not only polished but hardened. I have a set of stripped nut and bolt removers that have teeth on them that bite right into the fastener and twist it right off, they work absolutely bitchen. So I purchased a size large one for just this application and it tore the teeth right out of that socket, it was not pretty. So I have just gone back to the age old method of using an air chisel to drive them off. While it typically screws up the old lock, it does take them babies right off. If you do not have access to an air chisel and the pre-requisite air compressor to run it you can either see if the local shop will loosen them for you or use a hammer and chisel and really do it the old school way.

Mark