As it was said, 99% of the time this is a leaking injector.
When the injector leaks fuel, it puts more fuel in the cylinder than is intended to be there. It will inevitably make it's way past the rings on the pistons, and run down the walls of the cylinder liners, until it reaches the crankcase, where it will accumulate. A lot of times you can smell it before even checking the oil. The crankcase ventilation tube that gives off fumes from the crankcase will smell like diesel. This is my experience with much larger diesel engines than on these tractors, I am not even sure if these tractors have a crankcase vent that is open to the atmosphere?
A word of advice. If your replacing 1 injector, do ALL of them. 7 times out of 10, if you only do the bad one, a few months down the road, the others will go. You have to remember the other injectors have just as many hours on them as the one that went bad, they likely are not far behind. The engine would already be torn down and all fuel injectors easy to reach, don't pay to have the engine torn down multiple times, replace all of them in one go and forget about it.
