I have suddenly developed an oil leak that is quite perplexing. This first appeared during a longer XC flight and now is persistent. I noticed the leak while unloading from the trip and discovered oil on the fuel step and belly. Further investigation I found a bit of oil in the lower cowl, on top of the air box, more on the left than on the right, however it appears to be blown up to the nose bowl. The oil will drip from the air dam on the lower cowl after landing.

I have an O-320 (no suffix; narrow deck) with 400 hours SMOH (and a fine OH it was). Prior to this event, the motor would not use any oil during the first 20 hours of a change and then would use 1 qt during the next 5. I have changed the oil at 25 hour intervals and the filter at 50.

I checked all of the obvious possibilities, i.e. Oil filter, fittings and front seal. No indication of any leaks at all, and the pulley in front of the front seal is as dry as can be. No oil on the windshield or prop. I did find the oil filler tube loose, so I replace the gasket and tightened to no avail. Also found the rocker cover screws to be 1/4 to 1/2 turn loose. Again tightened but still leaking. No indication that the pushrod shroud seals are leaking. No oiled or wet areas on the motor or accessories.

It is true that a little oil goes a long way and I may be loosing a quart in 5-10 hours. So, what else can I check?

Thanks