How bad is it? I remember reading that some pulsating is normal for these displays.

Mine was similar. The corrosion was so minor that I thought it had been all cleaned up. It wasn't.

My headaches didn't stop until I did the reset modification, which replaces something like 20 components with one plus a few jumpers. i got my MCP130-460DI/TO on Amazon for two bucks plus $3 shipping. Had to wait about a week.

https://www.amazon.com/gp/product/B00AZV9CB2/ref=ppx_yo_dt_b_asin_title_o01_s00

When I started removing parts the problems became obvious. At least three old components were held together with nothing but friction... resistor leads fell out of resistors, and none of this damage was visually apparent while soldered onto the board. You may think all the corrosion is gone but there still might be parts that are compromised and internally corroded.

I was so happy with the MCP130-460DI/TO, I purchased a second one and put it on the driver board for a clean looking anti-thunk modification.

All that being said, I only had one boot problem with many weird symptoms. Whenever it booted successfully, I had zero issues no matter how long I played. However, it did not always boot. Sometimes it sat there with garbage on the displays, sometimes the displays stayed dark, sometimes coils locked on. Whenever I worked on the board, I thought I was making progress. However in reality I was just physically disturbing broken components elsewhere and the symptoms morphed or it would start working again for a little while. I mistakenly thought "I found it" at least three dozen times before I actually replaced the reset circuit with something reliable. All that wasted time and money chasing ghosts instead of just literally getting rid of anything that was touched by the alkaline.

I never lost the clock, but I thought I was having clock issues (some misleading info in an online guide) and I replaced the crystal and two chips... my symptoms morphed greatly but the booting issues persisted. I am still glad I changed those components because they were not expensive and now they're brand new.

The reset modification was so super ridiculously easy. There's a color coded guide and it's just a matter of removing those parts. Use existing holes to solder in solid wire jumpers and the new reset chip. Super easy and so glad I did it.

As far as your board... it doesn't matter how good it looks because we cannot see inside components. A couple of my 4 transistors were disintegrating up where the lead attached to the body and I could not see it. Leads fell out when I removed them. Resistors falling apart when I removed them... everything looked good at first glance, just like your board. Speaking of your board, it appears like a couple of your resistors are physically damaged... is the coating chipping off? Are those cracks where the leads enter the body? Get those replaced for sure, but at that point, might as well do the reset mod.

BTW, why is there a battery on your board when you said you installed NVRAM?

damaged resistors?

reset mod

What are the chances that 5 out of the 6 connector pins are loose on A1-J3 ? That seems to be the only other thing common to digits on player 2 and 4 since they share these wires. Is Z24 getting a solid ground and 5 volts to its corresponding legs?

On mine, I had a cracked copper trace coming from an edge finger. Could only see under magnification and it was causing intermittent problems until it failed outright. So just because you have new clean shiny pins inside the edge connectors, doesn't mean the connections on any particular board edge are clean, solid, continuous, or good.