Oil disappearing and reappearing

[shovel_head2001]

2003 Legacy, 2.5 liter, 5 speed with 231,000 miles. Very well maintained. Oil changes every 3000 miles or less (Castrol 5w-30). It has no apparent leaks, wet spots on the bottom of car or on the driveway and does not appear to be burning oil out of the tail pipe (no blue smoke at all when I follow in 2nd vehicle and no oily residue at tail pipe). My wife does however notice an oily smell very randomly and sporadically while driving but it doesn't last very long. My guess is that its leaking down on exhaust somewhere and burning off leaving no wet spots. This car seems to be low on oil about every 600-800 miles or so (Sometimes it wont even register on the dip stick). I will add any where from 1-1.5 quarts then drive it 50 to 100 miles and check the oil level again. At that time it shows it's over full by maybe 1/2 quart +/-. I believe that the engine may be burning a little oil but not that much (as i said before it doesn't smoke at all). I've replaced the PCV valve at the last oil change and the plugs have about 40K on them. Next I am going to do a compression check, look at the spark plugs and check all of the oil lines to the PCV valve but I wanted to see if anyone had any other ideas or suggestions. Thanks

[Fairtax4me]

These commonly leak oil from the separator plate, which is part of the pcv system, inside the bell housing. Oil leaks right down the back of the block then down the front differential case and lands on the y pipe. This only leaks when the engine is running unless it's really bad.

 

Other common leak points are the valve cover gaskets, cam seals, crank seal, oil pump housing to block o-ring, and an access cover inside the engine bell housing.