Flintstones: pop bumper part, and replacing the drop-bank opto

I received the parts for Flintstones:  a metal yoke plate that had been noticed missing from one of the pop-bumpers, and an extra opto for the one that seems to be flaky on the drop-bank board, registering false-positives.

I had never taken apart a pop bumper before, and kept trying to see how little I would have to dig through to get it in.
I found this video very handy:

The game was playing fine, but I imagine with that supporting metal yoke it would wear and fail far sooner than if it was properly sheathed in place.

Here it is almost fully reassembled.  Need to attach one last nut on the right, and align the spring properly.

the drop-bank assembly, with the opto board removed, just chillin' out beneath it.

I had never desoldered anything before, and after much struggle I finally managed to get the center opto out!
I was using a solder sucker at first, but a friend reminded me to use a solder wick with flux and that did the trick.  I was worried in my clumsy attempts that I had charred some of the traces, but in the end everything tested fine.
My solder joints were little unsightly blobs, but I got out the multimeter and did connectivity tests and everything was lined up the way it should be.

my glorious tools

The plyers acted as a great stabilizer for all this.  And yes, I did trim the wires a bit.  :)

So now the middle opto is not giving false-positives!  I put it back in the machine and it's great!
Only problem?
THE TOP OPTO IS NOW FLAKING OUT IN THE SAME WAY!
Drat.  What could it be?
Could the top opto just have developed the flakiness suddenly?
If there was a problem somewhere else, by replacing the center opto how could the issue be exchanged to the top opto?

What a mystery.  Maybe I just should have paid the money and bought the replacement board...  but I did order a 2nd spare opto, so maybe I'll take some time and replace the top one too.  *sigh*


DONE
fix always-down 'K' drop target
Installed metal plate for underneath pop bumper bakelight
Replaced opto on left 3-bank drop target PCB

TODO
File down mushrooming on upper flipper (bottom two were done)
extra GI mods:  lights in the city plastics, dinosaur plastic
Fix broken 3-bank drop target PCB, scores 800,000 points when flipper/shooter solenoids drop the voltage.