Hey guys-
Years ago in previous employ
we used to scrape off the varnish, score the rib with a checkerboard pattern, and crazy glue the leather bumpers on. Always seemed pretty nasty to me. The problem is that a material like wood or leather will not glue on to a varnished surface well. What I have found to work well is thick neoprene glued on with contact cement. It does not harm the varnish and if they come loose the player can reattach them by themselves without visiting a luthier.