Technical Intermittent non-starting

[Juliann]

Yes, that's the spring washer that's supposed to hold the contact ring on the solenoid wire tight against the terminal on the starter itself. They often rust apart, so I used rubber o-rings behind (or in place of) this part.
Unless your starter is actually faulty, try cleaning the contact surfaces on the solenoid and contact wire as well?

Not the easiest parts to reach unfortunately

Thanks; it “feels” unlikely that the starter/solenoid are at fault given the infrequency of fault and lack of clicking etc… Confident it’s a rust/contact issue so we’ll follow your excellent advice. Thank you again