[DanEC]

Greg - what I used from Home Depot is a Flush Valve Shank Washer by Fluidmaster, Part 89170. It's in a green and red blister pack. Here it was in the group of flush valve and toilet bowl valves parts.

I think I put a thin bead of 3M strip caulk around the pipe where it came through the body to seal it tight and that helped hold the washer in place against the body curve.

If you can't find one there let me know and I'll send you one. They are only a couple bucks.

Dan