MAJRob
I'd venture to guess that one of your trough optos is giving trouble. Check for cold solder joints and/or dirt on the opto units. Also check the header pins on the board as well as the IDC connector that plugs into it.

And now I'm in the club! Yes, the machine was properly folded and tied down during transit, but I had to snap a photo with the important details showing. Wish I had put it on the cardboard first - it was imamaculate.

IMG_20180722_151109225 (resized).jpg

All right then, so first question of my own. Is there any one likely point of failure that would prevent the flashers from working? All voltage LEDs are on in the backbox, the power driver 12V connector shows voltage, and the return from flasher to aux driver board shows continuity. Just checking if anybody knows of something that could come disconnected (or would likely be broken) before I brave the jungle and try to trace the individual power wire.

Yep, checked those - all of them are good.

I've noticed that the upper Rocks shots are not always lit. Does it give the full award sound for you, or just a more generic award?

Unlit: "Duh-DUM!" and a points bonus.
Lit: "Duhduh-Duhduh-DUH-DUM!" followed by either radio static or the "Extra Ball Lit" bells.

I'm not actually sure what determines whether an award is active or not, but it's by design. It's why the awards are denoted by light bulbs that can be either on or off.

Edit: Also check your feature menu adjustments, maybe something is disabled or set for hard difficulty.

Found in the rule sheet:
"Hitting the Center Loop at any time also lights the next unlit Flying Rocks shot. In any event, the shots are always lit in order from bottom to top, and you can collect only one EB from the Rocks per game."

The Center Loop is the shot to the right of the Bulldozer that comes out in the bumpers.

https://www.ipdb.org/rulesheets/1972/ROADSHOW.HTM#Flying_Rocks

Incidentally, I didn't know this! Now I do.