Thank you for the tips.  I've done most of the things you have suggested already except for allowing the time you described.  I haven't used penetrating oil in years and I don't even know if I have the right product.  I'm using 3 in 1 now, but I think what I used to use was just called Penetrating Oil.  I also don't have the best screw driver.  My heat source has been only a hair dryer on a modest setting.  I'll give the soaking more time and try a hotter setting.

Your suggestion of a Dremel tool is a good one, too.  I think I can borrow one and try that.  I can also grind the screw driver blade to fit a little better. Thanks again for the suggestions. You've been a help.