I could do almost a full day of towing skiers and wake boarders and occasionally a tube pull here or there on a full tank of gas, so something is up with your fuel consumption I think. My engine has more hours on it than yours and I do not consume any oil, at least I did not at all last year. I do not run full synthetic in my boat engine though so that might have something to do with it. I know that Mr. Hunter who has two Comps and a Sunsport all with the 351W engine in them runs synthetic so he should be able to chime in on that one.
'86 Comp TS6M - Reborn 2016
Riding a HO Sports CX Ski