THE VERY best way to avoid broken studs is to heat the nuts before trying to turn them. A gas welding torch is probably the best, but arc weld is a very good second. For all the hassle it saves a cheapo set from Aldi is good enough. A normal plumbers torch is not fine or hot enough to have any useful effect.
HOWEVER - ALWAYS disconnect all cable connections to the engine and disconnect the battery before arc welding. Forget and something expensive will fry just as happened on Long Way Round, but the same rule applies for all cars and bikes.
Its initially a bit more hassle (and dont weld so much the spanner wont fit) but its 100x easier than having to drill out broken studs.
When done use stainless dome nuts to keep the threads clean.
I wouldent use a welding torch or you'll have no head just a molten alloy blob!!
