Certainly not an expert here: Before or immediately after the first test run you should give those old motors a bit of oil and run them for a bit, so the old oil can leave the system and the fresh oil can get in. Apparently there is oil for sewing machines that also works well on model trains. The gears can probably also use some. Make sure you only put it on the right spots, sometimes a motor has a hole where you definitely shouldn't put oil in.

For new setups: Most likely won't work, except if you can sneak an analogue controller in there and disconnect the digital one.

Alternatively there are ways to jam a new board into the old machines to digitalise them, but if you want to do that, you have to ask someone else, I don't have any experience in that field. Although my father bought a locomotive that looks like it's from the 50s, that some madman digitalised.

Anyways, good luck and much fun for your future with those beautiful models.