just getting to the bottom of a dicky starter motor. 12v spins it up nicely, and having removed the solenoid and given it a good clean, 12v across the electromagnet seems to work fine, moving the plunger consistently. Before reassembling I was wondering whether I should apply any lubricant to the copper plunger. It’s a snug, smooth fit, Im guessing any grease will only eventually clog it up after time, and I should rely on the natural lubrication of the copper yes?

Not sure what you mean by natural lubricant tbh but I would not grease it or oil it as it will clog as you note
Is it not sealed anyway from the elements?

I bet there is a specialist oil for said job though I have no idea what it is

By copper you are describing the phosphor bronze bush, slight smear of grease won’t do it any harm, note the slight smear. The only thing you should be seeing is dust from the wearing of a clutch. The one thing we see regularly killing starters is failing dual mass flywheels, but depending what vehicle you have that won’t be a problem as it may well be on a conventional flywheel.

its inside the starter motor body which only opens into the bell housing to the flywheel – which is not lubricated either, obv, because of the clutch plate.

I mean lubricant as in the low friction of the copper (or its alloy perhaps)
like brass in a trigger mechanism for example.

No ..don’t use lube

phosphor bronze sounds right.
very little muck in there after 25 yrs (land rover)

but a bit tacky to touch which I think was the problem with intermittent engagement of the drive sprocket with the flywheel.

Conventional flywheel in that, not bad to get the starter motor out on those.

LOL

I cheated.

Ive taken the entire body and bulkhead off first 🙂