Along with the updated, stronger housing, you can also replace the soft alloy metal portion of the mount with a FMA PEQ-15 steel replacement mount. Around 18 bucks. It will take some fitting, as the two footprints are not the same, however, with a little work, you can upgrade the mount into something approaching ATPIAL quality.
With a newer series housing (75000+?) and a FMA mount, the mount shifting problems should be solved.