Diesel 310 brake system fix report
Probably no news here, but the sticking brake problem in my 83 310 is fixed, cause was the usual first suspect (master cylinder).
I thought it was due to collapsed rubber brake lines in the back. I thought it was only the back brakes that were sticking. Replaced them all (there are three: one on each wheel cylinder and one between the steel line that comes from the front and the steel line that goes to the wheels). Mechanic was sure there were only two, I told him I wanted all three changed, but I had to take him under the coach and show him where the third one was. No, it isn't a differential breather tube, now change it!
On the test run the same symptom came back, even more quickly. It was a nice day, so I got out and carefully checked all four wheels and sure enough, all four brakes were hot, not just the back. Replaced the master, now all better (and two flush/bleed cycles, ought to have all the factory original brake fluid gone by now!). And cracking open the bleeder on the front right wheel released the brakes all the way around (yes, it was in park and chocked, I am learning...)
I have the old master cylinder here and will disassemble it soon to see what happened. Shops these days aren't really equipped to do anything but r&r but we'll see what went wrong.