Try soaking it in Oil (WD40 etc) for as long as you can stand not to fiddle with it (I managed less than 3 days). Then either chase it round (but don't go nuts) with a hammer and cold chisel (read screwdriver) or if you can get the right tool to grip it then use that with a piece of pipe to act as an extension bar. It worked for me and I haven't done any damage. If you are worried about scratches then put masking tape around the tubing, not fool proof but can help!
Try soaking it in Oil (WD40 etc) for as long as you can stand not to fiddle with it (I managed less than 3 days). Then either chase it round (but don't go nuts) with a hammer and cold chisel (read screwdriver) or if you can get the right tool to grip it then use that with a piece of pipe to act as an extension bar. It worked for me and I haven't done any damage. If you are worried about scratches then put masking tape around the tubing, not fool proof but can help!