Registered: 02/09/16
Posts: 5791
Loc: Central New York
Take your rig down to your local NAPA or auto parts shop and try till it fits you. I'm sure they will help you. Just my opinion, hopefully it helps. Best way I see to find the best fit for you.
I found that a 3/16 x 1 3/32 #20 O-ring fits pretty close. The ones I found were sold by Danco Co., Concordville PA 19331 (made in Taiwan). This size fits pretty tight but was the closest I could find.