I opened it up and ran it through the dishwasher to no avail. Same symptoms present as before.

This looks to have been stored very badly sometime before I got it. There's some rust on the bottom plate and a lot of corrosion. The worst parts are fairly close to caps on the component side, but there's a lot of it all across the solder side. Most of the thruholes are solid green and almost all the connections on the underside are corroded to some extent, so cap leakage can't be wholly responsible.

Will my 8500 board fit in there well enough to test the speaker, CD, FDD and HDDs? 7100 board?

The PCBs of the HDDs also show corrosion. :-/

Worst case scenario is an empty case to support the MacCoffeeTable™ and a 40MHz 68040 for the 605+ or maybe a Rocket44 . . . }