Tractor Repair: 444 international tractor, international tractor, oil pan

Question
What would cause diesel fuel to get into the oil pan of a 444 International Tractor? It also smokes very badly.  And if you pull the dip stick out to check oil diesel fuel and oil squirts out.

Answer
 If this engine has a mechanical lift pump to pump the fuel from the tank to the injection pump, the lift pump could be leaking internally which would allow fuel to get inside the engine.  There's a very small chance that the injection pump could leak also, but the lift pump is the most likely.