Hi,

If all else fails and you wish to go a little further to save the caliper, this will work.

Heat up the entire caliper by any means available. I use a large propane torch, also known as a weed burner, tiger torch or rosebud, depending on who you talk with. Heat slowly without localized heat, as if you're baking it. In a pinch a Bar-B-Q or even a campfire will work as well. You could use your oven, but I guarantee your wife wont like it.It helps to have a pair of sturdy tongs.

At about 400 degrees F a yellow flame will come out from the brake line holes and last about a minute. That was the O ring burning. When there is no more flame or smoke coming off the caliper, it's done.

Set it aside to cool, and the pistons will either slide out with gravity or you can pull them out with your fingers. As a bonus, most of the rust will have disbonded from the surface, and the bleeders will be free.

Good luck,
Peter