Jerry,
Sorry it didn't work out. I once mounted a "no name" side mount and couldn't stop the top part from slipping forward, until I installed a roll pin through the dovetail for the top to bump against. Since it was in a dovetail, I had to first mill a flat( like a spotfacer)to keep the drill from "running". Whether you modify your mount, or not, is entirely up to you. It worked in my case, but I have no idea about yours. The mod is unobtrusive.
Mike