The final saga...just in case anyone cares, The O-ring that fits is a
M83248/1-015.
i care! bringing back this old thread to say THANKS.
mine started leaking recently and a search here quickly turned up Deano's thread and solution. appreciate the quick, easy and cheap fix. picked up a few -015 o-rings and no more leak.
BTW, 90 Duro Viton or Buna-N are probably the best materials for this specific application.