Replace wheel cylinders

When you change brake shoes the thicker lining of the new shoes will push the pistons further back into the cylinder. If there is rust back there then a leak will develop. At least pull cups and pistons to check and clean out. But like abodyjoe said the new cyl. are so cheap, it's better to replace. Soak the flare nut at cyl with PB Blaster or other rustbuster before trying to loosen.