Why can't rust take a day off some time?
Heat and penetrating oil and wiggle and pull.
My frame was rusted thru in quite a few places so I was replacing it, all I needed to save was the connectors. A hammer and cold chisel made a quick job of separating the pieces with the frame held in a vise. A new frame was $450 3 years ago so the condition of what you have and your budget may warrant a more judicious approach.
Steve
