Well, I ended up having to take it to a shop. With 160k miles on the original struts, the struts had essentially fused to the post. Apparently it took the mechanic 10 minutes with an air hammer to break it free.

I'm glad I didn't spend any more time than I did trying to get it off myself.

Thanks for the repair instructions. I had it supported on one side, I'll move the support to the center of the rear axle beam. Lets hope penetrating oil is my problem, and not a fused or rusted bushing. I'll get after it again today. The right hand lower bolt is stuck too, so if penetrating oil can'...

I'm working on replacing the rear struts on my '03 5 speed. However, I'm stuck trying to remove the lower strut mount from the threaded post. The rubber gasket seems stuck? I've tried prying it off, but it doesn't want to move more than a few mm before settling back to its original position. What am...