I use Ballistol. It's a great lubricating oil and corrosion protection oil.
I used to use Hoppe's Oil, it was a good lubricating oil but horrible for corrosion protection. My G23 is an older one that has bare steel frame rails, one of the frame rails had a small spot of surface rust develop on it while it was literally dripping with Hoppe's Oil. I cleaned the surface rust off and have used Ballistol ever since, and the rust has never returned.
I also found some very light surface rust in the internal areas of both of my slides, and I'd always been told "No oil in the slide internals". Well after I cleaned the surface rust out, whenever I detail stripped I started wiping the internal areas of the slide with Ballistol, then wiping them relatively dry. The rust hasn't returned since.