Yes - I took the solenoid board off some while ago and resoldered all the pins in the hope that would solve the problem. As that didn't work, I started replacing crimp pins and then shifted to replacing the header pins and replaced the long, brown one on the right hand side (see pic) this evening. The rest should go quite quickly as I am getting familiar with the process and there are less pins to deal with. Should have new header pins installed and the board back in the machine by tomorrow.

Crimp pins seemed "normal" albeit a bit tarnished, but not overly squashed.

How do you spot a cracked joint?

Have you actually pulled the board out of the machine and checked for cracked solder joints on the pins?  Not impossible that the header pins are the problem.

Whilst the crimp pins may not have looked damaged, I can assure you that after 30 years they are not like new and should be replaced.  Did you notice whether the old pins were flattened compared to the new ones you put in?

My guess is that once you remove that board and inspect the back of the header pins closely you will find cracked joints which may well be your problem.