I originally presumed you had a bad fader booster amp (the triangle that comes after the fader in the block diagram...U381 on the BUSS B PCB), or a bad component or faulty trace or solder joint associated with that amp because it feeds both the PGM out jack as well as the PGM signal to tape, and you have a problem with both of those. I'm not certain yet, but I think there may be two separate issues, one each associated with your two problem areas. This is why we take things step by step because you never know when your problem might have more than one cause.
The testing we have been doing is to affirm signal is getting to the fader (measuring between pins 7 & 9 on the fader connector), and then checking to see if signal is coming out of the fader (measuring between pins 8 & 9...this signal level is bound to be much lower than coming in...this is the nature of an audio resistor which is what a fader is and why there is an amp on the back side of it to boost the signal back to nominal level), and then seeing if the amp is outputting signal (pins 5 & 9 of the yellow connector J111).
To be sure we compared results to a known good path (I picked PGM 1). Things seemed normal. So I had you measure at the output jacks (which is the other side of the output path from the fader booster amp U381). As expected, PGM 5 is nil. So I had you back up to where the jacks connect to the BUSS B PCB and you've got signal there.
Look at the schematic when you read through my explanation above so you can follow along. The schematic only shows detail for PGM 1 amplifiers because the rest are the same, just different component numbers, so use PGM 1 as your example.
So let's start with what is likely to be a more simple problem and deal with the output jack. You need to set your meter to continuity and measure point to point from pin 5 of P109 to pin 5 of J109 (the connector), and then keep going (one probe stays on pin 5 of J109) until you no longer have continuity. I don't have a 388 so I can't guide you better than that but just connect the dots. My assumption is the wires from P109 go to a PCB to which the jacks are mounted. Just trace it out. I suspect you have a bad solder joint. I'll try and explain further if this doesn't make sense.