I have been using an ultrasonic parts cleaner on my cz’s and every metal parts of my fireams that will fit my cleaner for a couple of years now. For my cz’s, I just remove the slide and grip. Heat up the solution and go for 30mins in the ultrasonic cleaner. Wipe off the solution after cleaning.
I use Lucas ultrasonic gun cleaner solution.
Petroleum based so no worries of rusting.
Have not tried Lucas on polymer frames, so no idea of the effect on polymer frames.