I have good luck with Marine epoxy filling stuff. Use it when I don't want JB Weld. Haven't tried in on a magnetic chuck, Mix some up and watch it next to a neodymium magnet. Currently using it to hold rear view mirrors on. Works better then the official stuff. You do have to leave an ever so light thickness between the glass and steel, so do don't "press" the steel tight against glass. Going on 3 years on two vehicles.
