If you have a good heat gun, that has a small tip, it will also soften the loctite. Lockwasher should have been sufficient and not used Loctite IMHO. If you use a tap, remember it may be metric threads. Use hardware prescribed by engine/muffler mfg whenever you can. If entire head of screw is exposed, and all else fails, you can probably cut the bolt head off with the Dremel. Be careful not to damage engine/muffler when doing this and keep ALL metal debris out of the carb and exhaust (muffler in the way I know). Keep plug installed.

Good luck

Bruce