That is why if possible the circuit should be disabled. Before massive buildup occurs.

Some manufactures like Volkswagon and Mercedes got caught to the tune of billions of dollars by electronically cheating and turning them off. After the fixes they will remain on unfortunatly.

If you car is a 123 model I would remove and clean the manifold. Then make the egr circuit non functional. It helps the engine in other ways as well. As the diesels get newer it gets harder to achieve. Disabling the circuit that is.It is very simple to do on the 123 models.