I've confirmed a dead -8 volts at the regulator so my next steps are to
> test and likely replace the rectifier
The absence of -8 V is caused more often than not by a short. You should be able to check what's going into the regulator, thereby possibly avoiding a lot of disassembly of the circuits upstream.
Usually, a dipped tantalum capacitor causes these shorts. Specifically, I've seen C1569 being shorted. It's located on the A9 Interface Board, rear side, near the middle and easy to reach and replace without removing the board.
With the power off, measure the resistance across C1569. If shorted, you'll measure anything up to about 30 Ohm.
You may temporarily replace it with any >= 20 uF cap with Working Voltage (WV) spec. of at least 15 V.
An obvious difference between early and late >=B250000 versions is the replacement of the vertical output amplifier, from an "integrated" version, to a discrete version.
Raymond
Raymond Domp Frank