Slow..Rider,
They can be a bear. If you fabricate a huge screwdriver blade that fits the slot nicely from a piece of flatbar, and heat the OUTER housing slightly, it should do the trick. After you heat the outer housing...not hot enough to change color, squirt it with some WD-40 or something, then take your homemade giant screwdriver with a large wrench at a right angle as a lever, and wiggle back and forth until it starts to move.
A small wire brush is great to dig all the crap from those internal threads before you heat them and squirt them with oil. Keep thinking positive thoughts as you do all this...it's a karma thing.
Stuart
