So today I decided to rebuild the right channel output section replacing transistors, resistors, diodes, and diodes using the same selection of parts I used for the left channel a few weeks back [see below]. This channel now appears to be sharing load across the rails much more evenly, albeit based for the moment just on idle voltage drop on the final set of emitters. I've set the bias on both channels around 5/-5mV. There's still a little bit of a slow drifting evident: around .5mV up and back over a period of about a minute. I don't know if this is the way the circuit always worked or something that could be corrected with more work.
Also put a fresh dab of thermal paste between the thermistors (#144-074) and the heat sinks.
Oh: and here's a photo of that nasty looking diode from the right channel along with the sandblock resistor which was next to it. I assume those greenish splotches are from the diode. Some water must have gotten into this amp at some point.
Parts used for output section rebuild:
PNP, #132-151: ON Semi MJ15025G x 2 (drivers): Mouser #863-MJ15025G
NPN, #132-152: ON Semi MJ15024G x 2 (drivers): Mouser #863-MJ15024G
NPN, #132-164: ON Semi MJ15003G x 4 (outputs): Mouser #863-MJ15003G
PNP, #132-165: ON Semi MJ15004G x 4 (outputs): Mouser #863-MJ15004G
Emitter Resistors, #139-105 (inductive): Ohmite .15 Ohm/5W, 1% x 8: Mouser #588-15FR150E (non-inductive)
Resistor, #144-079: 12 Ohm/.5W x 2: Mouser #603-MFR50SFTE52-12R (metal film)
Diode, #070-031: 1N5394-E3/54, 1.50 amps, 300 Volts x 6: Mouser: #625-1N5394-E3/54