Sometimes, back to back presses work fine, no problem. But so much of the time is this constant pressing until it finally registers.

Remember you told someone that instead of turning the LED lamp around, you switched the wires?
If I were a betting man, I'd wager you broke a wire inside of the tab covering and it's barely hanging on.
Check all of your yellow/black and Black/Red wires that go onto the switch for a break in continuity.
Get yourself a good digital multimeter to check for continuity.
Your eyes cannot see under the vinyl wire covering.

If you don't have a multimeter, go into the tests for each individual button switch and wiggle the wiring as you perform the test.
If wiggling the wiring makes a button switch act funny, that wire you wiggled probably has a break inside the covering.
Something shorted on your switches before because you said that the contact tabs were all blackened.
That could of hardened the copper strands inside to the point of extreme brittleness, and therefore a possible break or choke in the wire crimped into the Push-On contact tab.
What I mean by "choke" would be by a wire having 4, 8, or 16 strands of twisted copper wire inside ( I don't know how many strands of wire are in there really) and only maybe 1 or 2 strands of wire hanging on to the Push-On tab, while all the others are busted...even hanging on by the vinyl wire covering.

The other two wires (Red and Blue/Black) are for the lamps...we don't care about those, and they wouldn't have any effect on whether the switches are working or not.
Those should all be on your switches, the exact same way...not screwed up. 

One thing that has always bothered me was these micro-switches.
They all have NO & NC tabs for "Normally-Open" and "Normally-Closed".
Why in the world would they put a "Normally-Closed" tab - which we would never use?
Even the IGT drawing of the micro-switches on the buttons isn't clear as to which tab is which. ( see below) 

If one Push-On terminal is on the wrong contact tab, that would cause problems with button operation.
Sometimes you might override the logic signal by multiple pushes (back to back presses) of a button....but normally the whole deck would be non-functional.

Your single black or double-black wires should always be on the "Normally-Open" tabs. 
Depressing a momentary deck button would thereby "Close" the circuit.

Click on button deck drawing below to enlarge if needed...>>>

Comparing your pictures, you did not receive your original MPU. There's only one dipswitch and maybe this board you have now does not support BV?

The little board where the input plugs for the monitor is the A/D board.  Basically it converts the VGA signal (which is analog) to a digital signal so it can be displayed on the digital screen (which is essentially any lcd/oled panel).  The fact that as it warms up, the signal becomes steady usually points to bad caps.

The following photos

Hi again. Ordered new microswitches, but I'm still encountering this problem. Here's a link to a video of me playing my machine and focusing on the Bet One Credit button. As you can see, this is a constant issue and I can't figure out how to resolve it. Sometimes, back to back presses work fine, no problem. But so much of the time is this constant pressing until it finally registers.

I need any help I can get on this. I'm just puzzled. Thanks everyone.

http://ec2-52-12-174-105.us-west-2.compute.amazonaws.com/IMG_9574.MOV