I have a Hunter 31 with a Yanmar 2GM. In the 2+ years that I have owned this boat, the engine has never used a drop of oil until recently, there has been (1) a noticeable drop in the engine oil level together with (2) an extremely oily main bilge (also never happened before). I notice only a slight amount of oil in the engine bilge water (i.e. from the stuffing box). On the Hunter 31, the main bilge and engine bilge are isolated from each other. Are these problems possibly related or just coincidental? What are the likely sources of each? Could the oil in bilge actually be diesel fuel leaking from somewhere and finding its way into the main bilge? Please note: the engine coolant remains full and clean, and I don't see any oil on the engine itself.