After landing at Fond Du Lac (Cheese Lake, WI) following the 2005 Air Venture Cup Race, I saw a clot of oil drop out of the left side of my cowl.  Knowing that nothing in aviation fixes itself (ever the pessimist), I pulled the cowl and noted oil coming from either the 2 or 4 cylinder oil return line area.  The # 2 return line hose-to-sump clamps were tightened.  Upon checking the oil level, nothing unusual was noted.  That puzzled me - How could that ugly clump of oil only appear from power reduction and landing since no excessive oil was used or apparent on the belly?

 

Several necessary following landings showed a similar "glob" of oil dripping out of the cowling, but the oil consumption was not extraordinarily different than usual. ???

 

Finally, I stripped her down in my hangar and began to inspect the cylinder 2/4 area and, Voila!  The #4 oil return hard line had been hack sawed thru by the safety wire that holds the two (front and back) cylinder head baffling pieces tightly against the fins.  Some 50 hours ago I had modified the #2 cylinder baffle (resulting in cooler CHTs) and rewired the material but passed the wire over the #4 return hard line rather than under it.  See the result:

 

 

That vertical line to the right of the double bend is just thru the aluminum - Of course, at WOT and 200 Kts, the wire was streched taut and kept the oil in the line - but - at low power, slow speeds the air pressure against the baffle was reduced, allowing the sawing and, ultimately, the leak.

 

$5 bought enough 3/8 tubing to replace the line and the local mechanic was willing to use his specialized tool to put the hose bulge in the left end (see above).  Installation was simple, but this time I passed the wire below (there was a "nick" on the lower side of the old tube) and secured it with those structural nylon tie wraps:

 

 

235/320/360 flyers, check that #4 cylinder head safety wire to ensure that it is not slowly cutting thru the oil return line!  I know I will check mine each time I remove the lower cowl.