Hopefully none of your guitars have gold hardware. Once upon a time I bought a brand new Les Paul Custom style guitar with gold hardware. Never played it and kept it in the case for safe keeping. About a year later I opened the case and the gold hardware was rusted. I've never stored ANY guitar in a case ever since then.
Wow! I’ve never heard of that happening! Your experience with your LP has to be pretty unusual.
An interesting thing is that pure gold doesn’t oxidize. It’s inert enough to stay shiny and perfect for 3500 years when they dig up Egyptian tombs and 2000 year old Roman coin caches; same is true when they find gold coins in ancient shipwrecks once the gunk from the seabed is removed, the gold is still shiny. So gold is a pretty stable material.
But whatever gold is plated onto can oxidize, and gold alloys can also oxidize, though it isn’t the gold portion doing it, it’s the base metal.
I’ve got 6 years with my Tonare Grand that has gold plated tuning machines; had around a decade with my Artist II with gold hardware, and certainly years with other guitars that had gold hardware. All were cased when not in use, no issues, no oxidation, nothing at all unusual.
My SG Special has been cased when not in use since 1965. The neck stopped needing periodic adjustments around 1972, and the action is still perfect after 47 years!
If I had to venture a guess, I’d suspect a problem with the plating on that LP, not so much the case, but who knows?