I would first get a repair kit for the guide pin and replace the old one. This is a fairly cheap way to start solving the problem. You dont have to bleed the system. At the same time I would push the piston in and pump it out a couple of times. Make sure it can not travel to far! Next step would be to take the caliper off and replace the piston after thorough inspection of the cylinder surface. I think you need compressed air to get it out. If the surface is bad (rust, pitted or similar)I don't know if honing will help. Ekkehart