Andrew, PM sent.

Thanks, installed a sleeve you very kindly dropped off, but unfortunately the problem is still there (and worse, really - less intermittent, which may be a good thing as it should be easier to troubleshoot).

Doing more testing, and EOS definitely is working at the switch level. (Normally closed and most definitely is; and it's actuating when the plunger operates.)

Next I will check the plunger for burring; otherwise I am looking at some sort of electrical or electronic fault I guess.