[IainG]

Hi
Most of the thread lock used can be released with heat.
I sheared my drive shaft bolt when I tightened it up. I think the thread lock actually locked the bolt so when I did the extra number of degrees rotation the bolt snapped. I was only left with 5 mm protruding. I applied heat(with MAPP gas blow lamp) and it just came out easily with mole grips.
So with yours once you have drilled the centre of the sheared bolt, if you can get heat on it, it might come out easily with a stud extractor. There are many grades of thread lock ranging from anti vibration(quite weak) to high strength(can sheer the bolt high) but heat will weaken or release most types.