Corvette: done?

After tonnes of research, a thread on MAACA and a more concise thread on Pinside, the problem seems to have disappeared after reinstalling the opto board.
WHAT. THE. FUCK.
So unsatisfying, but I guess I'll take it?  Might just be an intermittent issue, but I can't recreate the switch matrix issue any more.  Onward and upwards?

The opto board!  I tested all three chips for shorts.

 for reference, here is the LM339 diagram:

I did one last thing to Corvette, maybe this is what fixed it?

Shiny new glass channel!  Yes, that is what fixed the switch matrix!