Do check the jumper wiring as mentioned by Roamin. It is possible that the transformer could still be jumpered for Japanese voltages which could account for weak flippers, kickers, etc.

I would guess the measurement is across pins that don't match the pinouts in pictures in posts 18 & 28.
Can you provide a photo of the jumper locations in the connector at the bottom of picture in post 25 -- the connector with the two black wires?
A photo to show which positions the wires are inserted into.

Looking at your 3rd photo - the two black jumper wires in connector are in the correct positions for 115VAC.
Your hot wire is gray and neutral is yellow. Strange choice of colors.
Difficult to tell if other wires are in right positions but if they're original than they should be OK.

You can get readings for your incoming power at the service outlet mounted on the metal panel.
You can get readings for your power into transformer at the gray and yellow wires at the plug with the two black jumper wires.
Careful with meters in these areas - 120VAC can knock you on your ass... or worse.

Appears to be a problem with the meter.
Once in awhile, you can pick off a perfectly good Fluke 77 on ebay for about $20.