Does the oil filter housing look at all distorted or swollen?
I am not familiar with Yanmar, but almost all engines have an oil pressure relief valve that is supposed to open & send extra oil back to the oil pan if too much pressure develops.
If this valve sticks it can cause the oil filter to swell up & distort & create a leak where he filter attaches to the block. If this is to occur, it probably will be on a cold start when the oil is thick.
Often the pressure relief valve is part of the oil pump, but it may be a separate valve on the engine, as I said, I am not familiar with Yanmar.