Drum brake backing plate question

Yes I believe there are seals. I made a pr for mine out of sill gasket foam.
I kinda figured there must be something used in there or why else is the groove there and the flange. I may see if I have some thick cork I can fit in there and cut the center to just slide over the spindle and seal it that way. I've looked everywhere for a number and description online and come up empty. Nothing in the repair manuals either. Time for do it yourself I guess. Thanks for your input.