Ducati Single OverHead Oil Drain Stat-o-Seal Kit 250 350 450

To replace 0400-92-010, the aluminum crush washers Ducati used on ALL ohc singles.  On offer is a complete set of six Stat-o-Seal washers, steel with embedded neoprene o-rings.

Yeah, aluminum or copper washers work ok, sorta.  THESE THINGS, though, are perfect.  Aircraft-quality-expensive, but your top end will be bone-dry around the oil line area, guaranteed.