Super Glue. Let dry 5 minutes and tap out.
If you have the availability, shape (lathe turn, before the need) a wooden dowel. Insert with wet glue, let dry, and tap or pull out. This is for a real over pressure load.
If it's just a case fatigue separation, as you described, then a tight fitting/oversize bore brush will work to dislodge the case.
[ 01-11-2004: Message edited by: djd ]