Yup. That rusting mag release happened to me when I first got my Shield a few years ago.

It was my EDC in an Alienwear Cloaktuck IWB. Saw it's share of moisture in South Carolina. It was never stored in the holster, shot monthly, and meticulously cleaned every time it was used yet still managed to almost seize tight.

Emery cloth knocked down the rust and white grease prevented a repeat.