I can't help with the removal, but Corrosion X applied to the frame with prevent the rust.
https://www.amazon.com/Corrosion-X-90101-6oz-Aerosol/dp/B0009E3T6E?ref_=ast_sto_dp
True Value hardware stores carry it:
https://www.truevalue.com/all-around-penetrant-lubricant-6-oz