Left Rear Brake Drum

Since I was unable to make progress on the power brake booster rebuild, and I found a place that would do it for only $50, I mailed it in.
In the mean time, I took a look at the left rear brake drum. It was pretty dirty in there - lots of road grime. That's not too surprising, since the brakes haven't been done in probably over 20 years. The rear brake pad had some uneven wear on it, which if memory serves me, indicates that the springs are unevenly worn. That's not so bad, since replacing the springs on both rear drums costs about $7. The brake cylinder looked pretty bad on the outside, but once I got it taken apart, it was in surprisingly good condition. There wasn't much fluid in there, which isn't so surprising, since the hydraulic system seems to have lost pressure. There didn't appear to be a significant leak in the left rear wheel.
I'm predicting that I won't find a definitive cause to the loss of pressure - the entire system probably died from a million little pinholes. If the rest of the wheels are like this one, the amount of fluid loss of all of the wheels was probably enough.
In any case, I am going to be replacing all of the brake lines. The disc brake conversion for the front includes brake cylinders for the rear wheels. Once the power brake booster is back from the rebuilder, and get the parts I'm ordering in, I should be able to start and get the work done in a couple of weekends.