I agree with the posts that feel the rear diff lube is the culpret. Also, you can't adjust your brakes by backing up and stomping on the brake. The only thing that "self" adjusts the brakes is using you parking brake. All of the adjusting mechanism are connected to the parking brake system. Pull the drum in question and clear all of the hard parts and replace the shoes and fix the source of the leak. I wouldn't try cleaning the shoes, they soak up petroleum all the way through. Good luck,
Scott