they were initially greased (not oiled) despite being called oil cam or similar names even in official literature.
only a VERY thin film of grease is sufficient and the only type acceptable is optical grease or else it will gas and condense elsewhere.
why i avoid grease lately...well it tends to get gummed-up when small amounts of dirt contaminate it or when the grease goes bad. graphite powder wont do that and its very easy to clean.
instead of opening the camera to get to the helicoids to thoroughly clean old grease like what i shown in my blog i just remove the scale and then apply some graphite powder if i have the need and my helicoid feels smooth again.
the downside of using graphite is sometimes the powder will run out and it will happen sooner than a greased helicoid. the good thing is its much easier to maintain. opening and closing cameras isnt good for the camera so you would like to open as less as possible if you can help it
there will be helicoids that will squeak whatever you do and they had to be lapped using fresh rouge or metal polish. lapping compound is not cheap where i am