I don't know how much experience you have on Robbies.
I have been flying a Raven II for a number of years and have noticed that every time I filled the oil to the maximum of 9 quarts I would experience a loss of 2-3 quarts a flight.
And the underside of the machine was getting sprayed.
With time I noticed that keeping the level half a quart above the minimum was ideal. Very low oil consumption and no big stains of oil on the belly/landing gear.
Probably this has nothing to do with your problem but since I fell for this myself (the more I put in, the more I would get spit out, and the more I would try to put in the next flight, and so on), I just wanted to warn you.