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My marine engines have consumed so little oil with the Mobil-1 15W50, I have not really kept track of the hours. My particular motors seem to like that oil. Equivalent to automotive use, at 50-mph a 100 hour run would equate to 5000 miles, and it's not unheard of to go through a quart in 5000 miles with older motors, especially if you are pushing it when you're running, along with a lot of startups an shutdowns. I dare say there are some that will go through a quart in half that much.
If you are consuming a noticed amount of oil, I would check the compression to see if the rings really are the culprit, and then I'd look at those valve seals. You can lose a lot of oil down the valve stems, the motor can smoke, and the rings could still be in good shape.
If the rings are on their way out, you can bump up to a thicker oil and use plugs that will help with the burn. I'd be sure to get an oil known for low ash when burned, not unlike the two cycle outboard motor oil. In the end, you'll have to solve this problem by getting into the motor and seeing exactly what the tolerances are, etc.