Or skip the "inside the cap" O-ring all together and instead go for the newly released:
TLR334000 O-Rings, Bleeder Shock Cap (8): TEN, 22
Instead. These are normal often used rubber o-rings that go outside the shock body, at the bottom of the cap threads. Much easier solution
Ther is an article in the 22 setup sheet db on Petit RC on this as well.