@YeOldeStonecat, honestly I don't think it was liquid damage.
You've got 3 DC rails in a PSU, 12v, 5.5v, and 3.3v. Each must operate within 10% tolerance. 3.3-.33 = 2.97v. Tolerance is ONE THIRD of a volt... that isn't much.
In my experience, as soon as the 3.3v rail becomes a 3v rail... board nope out of booting. DC rails will drop voltage under load, and will not directly appear when tested with a volt meter in all cases.
Here's where things get fun...
PCIe uses the 3.3v rail for signalling. So does the CPU. So if that rail gets weak, and you put 2 GPUs and a CPU on it... well splat. So when you started mentioning changes in behavior as you shifted the GPUs around, I'm going to assume the 3.3v rail is FUBAR. And that, happens just due to time and age. It's the smallest voltage, with the tightest tolerance, age widens tolerances, ergo... this is the normal way for a PSU to go!
If water / salt kills a supply, that will typically cause an arc fault on the 12v rail, if THAT happens... machine is junk. Anything connected to the 12v will fry, which is pretty much everything. I've seen such machines become rather impressively long lived blow torches, it's spectacular! But also quite devastating.