It's not really a fault of any kind with the rings or warm up in the case of the EFI YZF's. If you were to take a healthy carbureted four-stroke engine of almost any kind and shut down following a good day's ride, let the oil cool and take a sample, you woud find little or no fuel in the oil during an analysis. But if you took the same engine in the same state and cold started it without then letting it run for a good 20 minutes or better, the same analysis would show a significant amount of fuel contamination for the exact reasons I described above. That's just how it works. The difference with the '10 and later YZ450 is that unlike the carb, which is manually placed in an artificially rich mode by pulling the choke, and then goes right to its warmed up engine jetting when that's turned off, the EFI unit will compensate for lower than full engine temperatures continuously all day long. When you combine this behavior with the fact that there is no thermostat in the system, and the current cold weather around much of the country where these complaints are coming from, conditions that cause the coolant temperatures to stay well under 150 degrees for the entire ride, you'll see extra gas in the oil because the engine is being run rich. If you either add a thermostat or cover one radiator, you'll bring the coolant temps up and the problem will cease. As far as injectors drooling, Yamaha hasn't had much trouble with that, although some of the CRF's have, apparently. As to how that raw fuel would get to the crankcase in a sitting engine, it simply drains past the ring gaps and down. No more complicated than that.