I have seen three 1965-66 Formula S blocks that have never had a cork gasket on the inside of the housing on the bolt. The cork gasket was no where to be found in two complete gasket sets that I have bought. The only time I seen a cork gasket was when I did research to fix this problem. Upon close examination of the adaptor and bolt the bolt threads into the block where it comes right from the oil pump then the oil has to go through the filter and then out of the filter to go up the engine to oil all parts. That is where the large round gasket seals those passages from leaking. So what I did is change the fiber washer under the bolt face to a nylon washer, used the large round flat composite gasket for the engine to adaptor seal with a little gasket maker on it. Tightened the bolt to just past snug, I mean a good grunt on the wrench past snug and everything is tight and clean, no leaks. This block was all boiled and cleaned before it was rebuilt so there was never anything in any passage or threads so that was not a concern and all gasket mating surfaces clean as a whistle. Where that cork gasket is would not seal threads to the oil pump very effectively as it is just around the bolt held tight by the housing pushing on it, any oil that would leak from the threads of the bolt would be so little that it should not be of any concern as far as filtered or not filtered oil. Hope this all makes sense to all of you but like I said it is completely fixed now with all surfaces bone dry, no leaks
