Ever notice that plastic coil sleeves are smooth ? During production - some EMs had copper or brass sleeves. Nice and smooth. Plungers are usually smooth as well.
Take any plunger and toss it in a tumbler. Install a new coil sleeve. You cannot get any better than that.
Dropping oil, grease or any other lubricant into a plunger was a method used by operators who did not want to spend the time to replace worn coil sleeves. In other words - it is a "short cut". It is also an advertisement and attractant to all the dirt dust and grime to accumulate on the plunger and act like "gum" over time.
Coil sleeves are cheap these days.. Cheaper than any lubricant !
