Now that I've studied the inside of the engine, and the passages through which oil can drain, I've observed that the crankshaft chamber must hold a lot of oil, as caricabasso says. The newer models have a forward drain plug, but I wonder, based on where it's installed, does it help to drain this chamber? The only way oil moves from this chamber is by having the crank splash it out, back and up over the transmission.
If anyone wants to see some pics, I've got them...
So, what about draining the oil from the sump, so it won't continue to circulate, and then cycling the engine - just a few turns - maybe without the spark plug installed to encourage faster turning, to try to throw some of that oil out of that chamber? Waste of time, or worth a try?