Sounds like a combination of a hung up piston in the caliper, combined with a sticky inboard pad. Generally, I would suspect trash in the cylinder bore, possibly from a failing hose.
My opinion would be to replace both calipers, as you can usually get a new/reman calipers for about the same as what you would spend on a kit + time spend overhauling. Plus, they'll have all new hardware and pins. On brakes, you always want to do the same on both sides to ensure even braking. A pair of hoses would be a good idea, too. For the lube, Permatex has a
synthetic brake lube that's the best I've used. It comes in a green labeled bottle, but it can also be found in small packets (like what ketchup comes in at the local burger place) in their "Counterman's Choice" rack. It's a somewhat thick dark green lube, real sticky. But it's very slick and stays in place.
One more thing, I'm not sure just how the mounting you're using is setup, but you might go over the areas where the pads ride with a file to square them up, sometimes that will make a pad hang up.
