I run the entire spring of a magazine through an oily patch, on new magazines and every year or two after that. The inside and outside of the magazine, as well as the follower, gets sprayed with Hornady's OneShot, then wiped clean and dry with a patch. No oil is applied. As mentioned, oil can migrate into primers, and it attracts dust and dirt. The wipe with OneShot does not leave an oily film. But it slicks up the mag (teflon coating) where the cartridge and follower move very nice.
I realized I do have a loaded 20 rounder for the Evo. That mag got the same procedure. Don't recall when it was loaded, but it's been months ago... maybe April? No cracks. I'm reasonable sure that OneShot won't harm it.