Looking through my NOS parts bins I discovered three different styles of foot peg rubbers. The ones on my early S/C slide onto a round (cross section) bar. The K6 has a rectangular shape hole. The earlier ones needed to be glued on or they tended to rotate and move on the peg.
One of my K6 pegs had obviously been “down”, the rubber end was mangled. Two passes with a razor knife and it came off easily. The “new” one is probably +40 years old (still in the Honda bag), hard as a rock. The hole appeared much too small.
I stuck it in a pot of simmering, boiling hot water for 5 minutes. It softened nicely and opened right up. Slipped down into place by hand, using an oven mit! After it all cooled down, it’s locked on, solidly in place.