A lot of smoke is not a good sign(worn piston rings/blocked breather/valve-stem oil seals/poorly seating inlet valves);however diesels with their high compression do get blow-back in several areas especially as the mileage creeps up....you only have to look in the inlet manifold/air pipes/air-boxes of most run-of-the-mill diesel engines when you strip them to see an oily sludge.

Check another example of this model for comparison.