See my reply to “Air in Fuel Lines”.

I’m not 100% sure on this but I believe o-rings are pretty standard now on the d-valves. Their only purpose is to minimize the amount of debris between the pipe and orifice. If t you don’t have them it’s worth considering. The smallest spec of dirt that falls in there next time you set the timing spells trouble. If you pull all your d-valves to clean and service the FSM also says it’s important to keep the respective parts separated as matched sets. If memory serves, the copper sealing rings under the d-valves aren’t typically replaced for the 616 whereas the 617 calls for new rings anytime they’re removed. I’m curious why but regardless they aren’t cost prohibitive.