i'll try to explain:
if you put lid flat on table and look down onto it, right inside the valve there are two small silvery washers, with a really small metal pipe sticking out right in the middle. (you can turn the lid upside down and this whole assemblage will move)
in one lid there is nothing, just the brass of the valve and a hole. At least this has answered the problem of not being able to keep pressure with this particular keg, but can them bits be replaced or do a need a new s30 valve ?

also are these prone to fall off on king keg lids?