Thanks deknow, that sounds like some good advice!
I hadn't given much thought to cold solder joints, cracks, or reflowing any suspect joints; great idea! You're probably right about the bipolar nature of the power supply back then, I haven't dug into the PS yet. I do have a scope and am going to troubleshoot it one of these days when I get some more free time. Will take some more photos then.
Luckily there only appears to be one custom IC in the machine and it seems to be working. There was a mouse nest under one of the keyboards. The mouse dug out padding from around the Leslie to make it's nest :( Luckily it didn't damage the Leslie and it didn't chew into the hundreds of wires around the nest. Thanks God!