I have a 99 F-150 which I purchased recently. It has 74,000 miles on it right now. It's the 4.6 litre. I bought it with 69,000 +/-. After the 1st oil change I noticed the oil was low, and seemed to be a quart low by the time I brought it in to my mechanic. I found a spot behind the oil pan (not on the pan), but around where the access hole is to where you might do a bell housing inspection. It was wet with what appeared to be motor oil. I have never seen spots of oil though. I brought this to the mechanic's attention and he checked it out and said there are no leaks and this was somewhat normal for that many miles.
Since the last oil change, the level has dropped maybe 1/2 quart in about 1500+ miles. I see no smoke, but can smell a burning of oil, but can't find any traces of this on the manifold.
A friend of mine looked at the wet oil behind the pan and said it could be the rear main. But my mechanic says no.
Any thoughts? thanks.

 

the 99 had a problem with the right side head gasket leaking oil at the rear. my 99 5.4 leaks oil there and has been fixed once but leaked again. i now live with it. it does not need topped off during the 3k miles between oil changes and it does not drip on the floor. it smells like burnt oil when i stop. i use a sync blend now so it doesnt smell as bad.

 

Very common. as long as it isn't hitting the floor you should be o.k.

my 99 does it as well and I have not had it fixed yet. I am waiting for the ESP to almost run out before I take it in.

make sure your mechanic only uses 6 qts of oil and a motorcraft or better oil filter. no frams or generic oil filters because they will make the truck rattle at start up

 

Have you looked to see if it might be the back of your valve cover gaskets hitting the y-pipe leaking from the top of the motor cause that happen to me one time and that was all it was
you can give that a try man