No surprises here. Everyone's pretty much covered it. Try penetrating oil first. If that gets you nowhere, torch the heck out of it. Obviously you want to be careful not to melt the rubber parts, but frankly when i get to that point with things i'm usually prepared to light some things on fire and just get replacements.

Plus you'll most likely have to work on freeing the slider itself once you get the bolt to come loose, and you'll want to make sure the other slider is moving freely, lubricate them both, etc. At that point, replacing a slider boot won't be a big deal.