I have two sets of cool head domes for sale . Good to go. One 19cc has a ding , didn't affect sealing at all.
Top pic = 19cc ding in the outer edge, worked fine.
20cc
$43 a set shipped (set of o-rings free with purchase)
pp for payment and US shipping only
also have partial o-ring sets for $ 8.00 /set. These include all except for the three largest rings . I never had to replace them anyway , just these .
Stud rings, dome rings, upper dome rings and the coolant spigot rings.