Oil Pan
Before you drop the pan, I'd look closely to try to find the source. Check under the transmission bell housing (also peek in the timing window) for signs of a rear crankshaft main seal leak and around the engine oil cooler. If you drop the pan to replace the gasket, you might consider new crankshaft bearings while you have access. You'd need to lift one end of the engine with a ratchet chain hoist to make bearing replacement easier. The engine is 2000 lbs. On the port engine, the main seal, pan gasket, and oil cooler gaskets/o-rings are standard JD parts.
If you need a new mechanic, you'll find more still working on these in tractors than in boats.