I've only been at it for approaching 2 years now. So far it hasn't been an issue. I do try to find a reason to give each of my working machines a little attention. It's not easy for me either. I started collecting with a small house that's already full so storage is less than ideal to put it kindly. I'm sure as I get more of my machines back into usable shape it will be a bigger issue. I prefer portable machines but most of what I find seem to be in cabinets. Cabinets are even harder to have set up where I can use them. I'm hoping that by the time most of my herd is operable I'll be able to build or get some shelves and have them all stored properly with easy access.
I think as long as you run the machine a little every few months you won't have any issues. It takes a long time for oil to gum up.
Rodney