In a PA 28R 200. I believe it's a Lycoming IO 360 C1C. I just noticed a small oil leak on the ground after a two hour flight. Looking up in to the front gear well, there is a small brass 90 degree fitting on the bottom of the engine near the oil drain plug which feeds a small (1/4 inch) oil line. I assume it's the oil line going to the prop control. This fitting is retained by a brass lock nut. Oil was oozing out of the fitting, and the fitting was actually loose (not just turning loose, but wiggle loose) within the locknut. I threw a wrench on the brass locknut to see if it worked loose but it was tight. There must be some sort of o-ring or seal in there that blew out. No oil appeared to come out in flight or there would be a big mess on the firewall and under the belly but I didn't observe any fresh oil other than in the immediate vicinity of the leak. I'm guessing that the fitting probably sealed itself in flight from the oil pressure, as it started leaking several minutes after shutdown. Or, it just happenend to fail as I was taxiing on the ground or as I was shutting down (seems unlikely but possible.) It's unclear how much oil was lost, there maybe an ounce or two on the ground. I checked the oil level, which was slighty over four quarts (I left with slightly under six quarts) but it was a warm engine and probably still draining down. Haven't got a chance to check the level cold again for comparison. Again, if I lost a quart and a half in flight I sure don't know where it went because I didn't see a mess on the engine or belly. Is this a normal condition? If not is it an easy fix, e.g. pop the fitting off and replace a seal? The Lycoming site is frustrating as it does have a parts list but no diagrams. Yes I know an A&P needs to fix it but I just want to get a handle on what I'm in for.