First off, at OVGRS we do not leave rolling stock outside to face our weather, where we get high humidity and the full four seasons of weather. We have an active fleet of over 400 cars, all with #1 gauge Kadee body mounted couplers.
We do find that the metal “tails” (simulated air hoses) on the couplers do tend to rust, causing the knuckles to split. So we very lightly lubricate the metal part where it enters the coupler, top and bottom. We use the Labelle plastic compatible “Gear Lube” with good results. We do not in any way lubricate the gear box part of the coupler which is just plastic against plastic.
We use the same gear lube for truck journals – again with great success. It stays where it should and does not
dry out and cake, like the often recommended “White Grease”.
For a less expensive replacement of Labelle gear lube we use an automotive “synthetic” gear lube, which is of the same grade as the Labelle product and is plastic compatible. It is the brand “Lucas”, comes in a quart container featuring a spout that seals and is small enough to refill our small applicators.
In all cases – couplers and trucks; only a small drop is needed, and the gear lube does not seep out, to collect dust and grime. We stopped using the oft-recommended “White Grease”, as we found that it dries up and becomes a powder, caked on outside of where you want the lubrication to be, while the gear lube stayed where you want it, to do the job, without drying out.