cranck case problems

[Chris KC]

Without a photo it's hard to judge but is there not some way you can apply some torque to it, either by grasping it with something or perhaps drifting it around with a punch? If so warming the case will expand the aluminium away from the tap & loosen its grip somewhat. It's not a critical fastening and if you make a mess of the hole it's fairly easily plugged and re-tapped.