Brake Info.........

Need some advice here and wether to act on it. Re-doing my rear drum brakes and replacing them with all new stuff. I was cleaning all the rust off my rear back plates, I noticed two oblong holes at the bottom of the back plates. They are behind the adjuster screw assy. and in between the brake shoe contact areas. They are cast into the plate, so no question that they are suppose to be there. On the driver side it seems to be like a rubber pad material on both of them and they seem OK with no wear on them. But on the passenger side one of the them, the rubber material has been worn down and I can see some daylight thru it. The other oblong hole there is wear but not all the way thru. Now is there replacement pads for these or do I ignore it. It seems that the metal on the end of the brake shoe assy. must sit on them and have worn them out. They must be there for a reason and I can't find anything in the service manual mentioning these at all. Need some good info. Thanks Ed........