Not sure how much room you have to get to the srtipped plug, but here's a few ideas. HEat the case area around the plug to expand it. Go to the next size and drive it in and try and turn it. You may have to make you a "wrench" on a grinder to fit it. Keep it hot around the plug area , if it doesn't turn heat and tap with a hammer. You may even have to take a dull chisle and tap it around. I have even did the heat and put my extraction tool in the freezer, to keep the plug cool and not expand with the area around it. ANother way is what was said above, although I am not a fan of easy outs at all. You can use a reverse ground bit( cuts counter clock wise) and some times it will back the plug out. Two things you are after, not to mess up the threads, and get it out. What ever works. I am sure it's in a place that's not too easy to get to. At least it always is for me! use anti sieze on it when you put another back in, and it doesn't have to be real tight.
