I don't remember any washers between the cooler and the case. That may be your problem.
Other possibilities include the oil pressure sender (as previously noted), or the O-ring around the part of the distributor body that pokes into the case. Possibly oil spilled while filling the engine up. (Don't laugh--one time I scared myself pretty good by doing just that!!)
--DD
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Pelican Parts 914 Tech Support
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