>> Does anyone have experience with screw/bolt extractors?  Do they
work?  Are
>> they brittle, do they break or crack leaving a half  broken extractor
>> inside the already broken bolt.

You might try filing a little grove in the side of the screw and using a
punch and a hammer hitting on the outside edge in the unscrewing
direction to try to break the screw loose. I used this procedure to get
a flathead screw loose once. It takes patience and make sure you don't
hit anything else :-) Obviously, this will only be feasible if you can
get at the screw.

Scott Semyan
'85 Westie