Justin, looking at the pictures I can see that the diode packs appear to be isolated from the chassis with mica washers and some thermal grease. It would be worth checking that the washers are not damaged (perhaps have pinholes in them or a piece of swarf punching a hole through them). Since the metal bodies will be connected to the DC rails, a short there will pull the transformer outputs down to a diode drop above the chassis potential, presumably ground. I don't know if this area has been disassembled previously but if the thermal grease has been replaced, somebody may have used silver loaded grease, typically silvery grey in colour, and popular for use with CPUs and heatsinks in computers, relatively cheap and very readily available. This grease is (highly) electrically conductive and if carelessly applied can bypass the insulating washers. The correct grease would be aluminium oxide loaded grease, which is white.

Just my 2 cents.
Phil