the exhaust gases are corrosive and I've seen pics of where it has eaten a bit of the head... my plan for broken studs that are flush with the head is to buy either a right angle air drill (seen them where they are less than 5/8 at the chuck but they require special drill bits that thread in but they are expensive... others seem to be right around 2 inches from the back to the chuck) or the Milwaukee close quarter http://www.homedepot.com/p/Milwaukee...=5yc1vZc27fZzv
and use left thread drill bits. talked to my dad (who has a car hauling business and a 6 bay shop but lives 1600 miles away) and he said to try and tighten them slightly before loosening them and don't use the screw type extractors... use the square ones ( like these http://www.homedepot.com/p/URREA-1-8...500A/202797903
) and also many times when you're drilling with a left hand bit, they will come out.
i've never had to extract bolts where i didn't have a lot of room and i've had a lot of luck with just drilling them with a normal bit and pounding a torx bit in them as an extractor.
edit: i also think i'm gonna try to warm the head around the studs with map gas (not hot just warm) and re-spray the studs a few times... don't know if it will work the way i think it will but i'm thinking it will be like soldering a fitting. you heat the back of the coupling and the solder wicks (not sure if that's the right term) all the way back. gonna try it Saturday so we'll see how it turns out.
I agree that even if kriol or atf/acetone are that much better, it's still not the same as soaking it in a bucket of the stuff... just trying to do everything i can to avoid breaking them. even if there isn't much chance of it making a huge difference, it's a small investment