Thanks for getting back to us, Joe. Unfortunately, we haven't been able to find a shim that can boost up this lock. The only thing I can recommend is packing it out with a few thick washers. Do you think that could work?
I have the same problem. Without the plastic piece there is nothing for the screws to fasten to. I'm trying using an aluminum epoxy to fill the frame where the plastic was, and drill holes for the screws into it. It has worked on one window, the 2nd window only one screw held, I think the epoxy was too soft. I still think it should work, maybe I didn't mix the epoxy enough for window 2.