I'm doing mine tomorrow the little booger was $105. 00 at the dealer. Seems reasonable after six years and 91k miles.
In my opinion, there is no need to ever replace this unless it's somehow damaged.
It's a simple vapor/oil separator, with no filter. It has internal baffles just like any other ordinary separator, and it's clear (to me) why Cummins never specified a replacement interval.
I've attached a photo where I tried to show inside the breather to show it's empty. It's upside down in the photo.
-Ryan
I think your right Ryan. However I've had it for awhile. . and don't think I kept the receipt.
See TDR Issue 60, p. 92 for a discussion on the crankcase filter in the valve cover (under the plastic cover) for 2003-2005 Turbo Diesels.