I seem to getting some air leakage around the tubeless valve. Should there be an O ring on both sides of the rim?
Nope. Tighten that one on the outside up good n proper. It could also be a leak on the tape anywhere round the rim but just escaping at the valve.
Yup, the washer on the outside of the rim doesn't do any of the sealing, check how the end of the valve is sitting on the outside of the rim but your rim tape is more likely to be the culprit.
I had this yesterday. So changed tape still leaking. Then put valves in sealant then inserted them, tyres on and quick ride round block and now ok.
I also poured in some sealant around valve inside then popped tyre on.
If the airs reaching the o-ring on the outside it’s to late, it’s just there to protect the rim when you tighten the nut.
If you have a fast leak, it’s probably the tape at fault. If it’s slow, go for a ride and get the sealant we’ll moved and see if it seals properly.