He needs to start by looking at the DS relay circuit. You'll notice in your print, if DS (NC contact 1) does not open, CS will not drop out. In my experience this is the most common cause for CS lock-up. Check out all contacts that pick up DS, CST, SE, SEA, and the DT TIMER. The quick explanation is as follows:
CST is picked up by CS and CC (car call) or HC (hall call)
CST N/O contact picks SE when car is in 2LR (door zone)
SE N/O contact picks SEA
SEA N/O and PA N/O contacts picks DS after DT (door timer) expires.
DS N/C contact opens dropping CS.
By going through all these contacts you should find your intermittent culprit.
Good Luck!