Hey Andrew,

Could be a couple of things. There are two reasons why the fluid level can drop 1. There is a leak 2. The shoes have worn. The way it is pulling sounds like you could have leaking wheel cylinder in the left drum which has contaminated the linings. You need to pull the drum off to check this. If both drums are dry inside check the linings to see how worn they are. If all checks out OK then try swapping the outer part of each drum over to identify if there is a prob with that like it's scored or beyond min diameter. Lettuce know what you find.