Drawer backplate

Plastic bracket at back of drawer hardware to hold slider in place. Existing piece has a large G with the numbers 6020 6 and either RH or LH after the number. We have located similar items but they are not large enough for the drawer hardware. Need opening approximately 1 inch by 3/8 inches. The inner part of the plastic bracket does not have any extra grooves or flanges where the drawer hardware will sit. These were installed in 1989 on all kitchen and bathroom drawers in custom oak cabinets. I suspect we will have others failing, although the drawer in question is the largest one of any that we have and probably carries the most load. Hope you can help.