Has anyone ever seen this? I have rust on my rear sight. I've only shot it indoors and the only thing I've ever touched it with is maybe a silicon cloth.

stored in case or humid area ?

In a case in the basement. I'm not sure what the humidity is down there but it's a finished basement.

The safety button has some rust on it between the ridges too.

Rub it out with some Rem-oil and put some desiccant packs in the case.

okay thanks.

Basements are notorious for humidity. If it is stored in a cabinet, use a Goldenrod. If not, a large size descendant and either change or renovate it often.

 

You might want to look into a dehumidifier in the basement area.

Rub it out with some Rem-oil and put some desiccant packs in the case.

 

Is Rem-oil a specific type or can I use any gun oil?

rem-oil is a cleaner/lubricant in one can. I think any cleaner would work, clp, rem-oil, good old hoppes #9 and oil, etc.

i would get it out of case + basement - use oil or wax to protect it after you clean off existing rust - wipe down to remove fingerprints before storing -