I have inspected the above remarks and find them completely legal. 

I am surprised that it would even boot at 3.64V 
sounds like a capacitor problem but could just as likely be a bridge fault.
even if it is the 5 volt reg if the original caps and bridges are still on the board the are due for a change.

If you have inspected the header pins and connector housings on the relevant connectors and, found them in good condition, with no brown scorched areas on the housings, and the wires are seated in the housings properly and they all seem fine, then the connections shouldn't be cause of the fault.

you can remove make sure that fuse F113 looks ok and has clean metal caps on both sides, then make sure the fuse holder clip surfaces look ok, when you re fit the fuse make sure it is sitting in the fuse holder nice and tight, if the fuse slides left and right really easy or one of the ends is sloppy then this could also cause problems.
The fuse holders on these boards are pretty good in general but i do find a loose one from time to time
 

I don't think its a varistor problem for the same reasons mentioned by DSB
Happy to have a look at it when i am in Brisbane next.