Finally got everything buttoned back up! I filed down the ridge on the sealing surface and got the (second) new seal installed with the help of the seal installation tool I bought (always helps to have the right tools). Got the new brake shoes adjusted and also lubed the rear spring shackles while I was there. Took the truck for a test drive and everything seemed to be working A-OK. Now I wait to see if the new seal stopped my leak. Thanks again for the help here!