I used to have that same engine (and boat too) and witnessed the exact same problem.
My solution was to keep the oil level at less than full. A full tank of oil is good for a full tank of gas - approx. 150 to 170 miles running. Filling it up to the halfway point was often good for a typical days trip. The oil alarm used to sound for me when the oil level falls to the last half gallon (50 miles to go), so adding a quart or two, keeping the partially full jug in the back hold, was mostly painless.
Also, I seldom tilted all the way up and over to the point where the locking support flipper was used. This was a trailer boat. For running on the trailer, I trimmed up so that the skeg had about 1-foot of clearance to the road, which was plenty for most ramps and curbs. If you're in a slip and have to trim full up and locked, then you're going to see that oil tank leak. It's a feature!