On top of engine but underneath the plastic cover there is a square black box that i'm assuming is a crank case filter / breather. Is this correct ? Is there any maintenance or replacement required ? How often ?

THanks

 

It is.
Mine has no filter it it, just the black box with the hoses hooked to it. So I'm guessing, No changing ever...

 

I think there is a filter in there but you just can't see it. I just had mine off and I sprayed a bunch of carb cleaner through it to try and clean it. I don't know if it did anything or not. One thing I had not realized is that one hose exits under the truck and the other goes back into the block.

 

Genos Garage has the replacement filter for the 5.9 up to 2005. The 2006 & 2007 5.9L does not have a replacement filter. If the 06 -07 plugs and / or dripps oil the cover must be replaced.