I'm with another poster, get some old Campy Skewers (records) and replace the outer locknuts on the hub to something better (hardened) with better knurling on the face. Another thing you might try it you haven't already is to remove the springs from the skewer and tighten it up without the springs. Maybe take apart the skewer and grease the cam parts for easier tightening but be careful you might overtighten it. I wouldn't trust and washer between the skewer and the frame contact.