I have an 0S 46 LA and the backplate that is plastic has one of the screws stripped,is this going to affect the performance?

No, but you are now relying on three to keep it on. I have a few where the metal around the hole is missing. The screw hole is deeper that the screw is long. I just get a longer screw for an easy fix. If its just the tab on the plastic backplate thats damaged, use a washer. Joe