Scotty, I have a 2003 Tacoma with 300k miles. I just changed the drum brake shoes and wheel cylinders. The pedal was spongy and went to the floor. I then bled each wheel, the BPV valve, and even the master cylinder, though not in that order of course. The car seemed to be close to what it was before, but the I heard a pop from the front passenger wheel (I did not touch the fronts except to bleed.) and it went back to spongy. I cannot see evidence of leaks of any kind. Kinda regretting even trying to mess with this stuff...

check for calliper problems on the side that popped

Turns out the popping noise was the self adjusting springs on the rear drums, I have bad hearing. The spongy pedal was caused by defective brand new wheel cylinders. Just threw the old working ones back on, car stops better than ever! Love your show