It's definitely for the 90* oil filter adapter/oil filter plate. Trust me. I replaced mine twice trying to get it to seal.
He's talking about the 90* adapter bolt. You definitly do need a gasket under the head. As it's a hollow bolt that directs oil through the 90* adapter.
View attachment 1715062433
As you can see from this pic. Oil flows up the center of the hollow bolt. And is directed through the two holes. Without a gasket under the head of the bolt and sufficient pressure oil can make it's way out and up the bolt and under the head. You also should have a gasket at the bottom of the bolt. The mounting surface between the block and the adapter is recessed where the bolt is. And without a gasket down there it won't properly divert flow up the center of the bolt and into the filter. Meaning most of the oil doesn't get filtered.
View attachment 1715062434
That's the job of the cork gasket. It helps direct flow up the bolt and through the filter.
Hope this all makes sense.
