check your molex connectors as they are prone to failure and fuses[fuse clips] they are known bad points. Also the 5 volts originates from one of the backbox bridge rectifiers that generates 12 volts and if its bad low or no 5 volts will be seen. Good call on the c2 and c3. Every data east power supply I have ever seen needs these replaced along with all connector headers and fuse clips reflowed at the very minimum.
As mentioned before doing anything check fuses and try to press the fuse in extra hard and if the holder splits it needs replacing.

I would check all the rest of the caps and traces. Failure there is very common when caps spill their guts and its easy to miss a bad trace. The 2N6057 transistor (replace with a 2N6059) could be bad and there is another chip [mc1723cp]in that circuit but barely ever goes that could be the problem.
But as mentioned any bad cap will drag the power down , I have had the little tantalum/ceramic ones go bad too and drag components down.. So double check traces and caps and good luck!

Anytime. Glad you got er fixed up! Always nice when a plan comes together...lol. Have a great week.