The seal I am lead to believe was never present on our engines or the zd30 patrol. It looks like it was in the td42 fuel filter head assy which has an almost identical appearance apart from the bleed screw, it also uses the z332 filter, hence like has the exact same dimensions, meaning Nissan like cut costs and used virtually the same mould on the zd30 as they did the td42 which had the seal seat. The td42 filter assy actually comes with the seal if you buy the whole thing. The issue with the seal on a zd30 filter assy is if you have a look at the filter surface where the seal has to sit against the filter body and its not a good sealing surface, it has curvature to it, unlike the sealing surface on the outer rubber ring which sits flush against the flat surface of the filter assy. But I'm sure there is no harm by using a seal in that spot, it's likely just overkill