Oil seal for head gasket -- use one per engine. Early gaskets did not use this.
11045-H1000 RING-OIL,OIL GALLERY A12 0672-
Used with gasket 11044-H3900 GASKET-CYLINDER HEAD A12 0671- The first year of this gasket, the oil seal was not used JDM B210 A12 gasket 11044-H3901 in 1973 did not use it.
EUR N10 Cherry (A10 engine) 1978-1981 used this oil seal
So it is needed? Maybe. If it comes with the head gasket, use it.