Analogue-sequencer

> Apart from some women's underware stuffed between the pot 
> boards, it looked identical yes.

I wondered where they'd gone...
 
> Okay, I removed the two ICs from the upper potboard (the one 
> printed 'Upper potboard', with no luck. Then I also swapped 
> the ICs on the lower board. No luck either. I get the same 
> repeating events from step #13.
> 
> Are there other options?

If moving the ICs leaves the problem in the same place, then the 
problem is either on the pot itself, or the PCB. Either could be 
affected by shock or dirt during shipping, although I would think it 
more likely the pot has the problem than the PCB.
How's your soldering ?
I can post you a couple of spare pots to try replacing them.
Until then, you could prove conclusively whether the pot is at fault 
by swapping pots on the same board.

Cheers,
Colin f