Have you checked the base that you have now? If not take it off and check it to make sure it's straight across the top if so then put it back on but only the front screws check to see of there is any gap between the rear and thr reciever, if not do the same to check the front.

If there is a gap between the rear of the rail and the reciever when you torque ot down you get a reverse cant, and to me that sounds like what has happened it's a easy fix all you have to do a bead the base.