Been chasing this issue for awhile, if anyone recalls I adjusted the booster pushrod before and it seemed to cure it for awhile. Master appears to be stock toyota. I had a poor brake pedal and even worse pedal height that basically no matter how much you adjusted the rear shoes it didnt change. I finally gave up and adjusted the booster pushrod and everything seemed fine for about a month. Pedal worked fine, was much higher than before and stopped well.

Fast forward to the other day and I noticed again, hmm pedal is low but truck still stops...Adjusted the pushrod again and its better but not great (didnt want to over adjust it by mistake)it baffles me why I needed to adjust it again.

There is no hissing, the booster is holding air it seems. Truck off pump up the pedal it doesnt seem to sink. Truck on, pump up pedal and yea it does slightly sink. I can barely fit my foot under it, when before I know I could easily fit a my foot with workboot (much larger than my sneaker today) in the gap easily after I adjusted the pushrod.

I think the seals in the master are bad, whatcha think?