Unused firearms get a disassembly, inspection, and lube/oil every 6mo or so. To date, I’ve never found anything wrong during an inspection but it makes me feel better.
On infrequently used firearms I tend to use grease on contact surfaces moreso than oil so it stays put better. Oil tends to migrate downwards due to gravity and away from the contact surfaces.
I have my grandfather’s Auto Ordinance 1911 that we found in a secret space he made in a wall in his closet. Found that, German Luger, Nazi flag, German money of the period, a Nazi pocket watch, a diary from a German soldier and various trinkets.
Guns not in use probably get a look every few decades, whether they need it or not — or if they’re being moved, or I just have an urge to fiddle with them. Clean prior to anticipated use or storage. I’m obsessive about other things.
I suppose if I didn’t have alternatives I would give myself more lead time to resolve unpleasant discoveries, but so far things have always been ready to go. Guns I expect to be ready for immediate use are a different story.
My location has little to no humidity. My war toys are stored in a bank vault in my garage with a de-humidifier, and are kept lightly oiled. They get pulled out and inspected every 6-8 months, usually this time of year with a football game playing on the radio or garage TV. Yes, I’m decadent.
The carried arms get fired monthly and cleaned when I get home.