You can back shoes off manually using the star wheel at the back of the drum although the automatic adjuster may set them back on again. I think if mine were binding I'd pop the drum off annd check all retaining springs are in place. I recently fitted new brakes front to back in prep for MOT and fitted all new springs and pins which you can get as a kit from GSF.
Slave cyclinders are cheap enough. I now fit a new one if I ever have cause to remove a rear drum and I can't remember when it was fitted. Either way, investigation is best.
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