One way I have used to get off stubborn parts is one of those rotary hammer drills.If you can angle it right it really delivers a lot of hammer force to the offending part. Heating helps (i use one of those plumbing hi heat blow torches). You can use the sds chisel bit but if you want to reuse the part it can damage it. Sacrificing a bit by cutting off the chisel gives a better impact surface.
