Crankcase ventilation filter
 

I have a 2005 Cummins and when I bought it it had a blown rear seal. After changing the seal, the diesel continued to smoke and use oil. I cleaneds the filter and the problem stopped. It has been about 1500 miles and every now and then the engine smokes and I can smell burned oil. How often should I clean the filter? I cannot find any recomendations in the user manual.