PART NO.  SPL.PAGE  DESCRIPTION                                                            
2K4982    15.A.9    Washer for cap nut -fibre (2) -(pressure relief, engine unit, 1500)
2K4982    sup.9     Washer -cap nut (2) -(fibre, oil release, engine unit, sup)
2K4982    16.A.29   Washer -cap nut (2) -(oil release, engine unit, 1600, 1622)
2K4982    TC.A.13   Washer for cap nut (2) -(oil release, oil.pump, engine, Twin Cam)

This is the fiber washer (2) used for the oil pressure relief spring plug.

If you don't like fiber washers there, you can substitute 6K431 copper crush washer that was originally used for the Twin Cam alloy oil sump drain plug. Many of the parts vendors seem to be making that substitution recently.