A & C,
This may not help much, but at my annual inspection last week of Sept, I replaced the valve cover gaskets on my Lycoming powered C-172, then added 7 qts of Aeroshell 15W50. I haven't needed to add since, still showing 6 1/2 qts. (app 6 hrs flight time since.) Strange to me too, since I normally used a qt every 4-5 hrs before replacing those gaskets....