Is the pump not pulling vacuum or is it leaking oil. I have never seen one fail but I have seen hundreds of them leak oil. If it is just leaking oil the seals and o-rings can be replaced. Not too hard to do yourself if you are mechanically inclined. Parts are available from the dealer and if I recall they are under 100 bucks.

Just checked with my parts dept, dealer price is $117. Or you can go to a Cummins dealer, bring your engine serial # and they cn fix you up for under $20. I have personally done this repair and have never seen a vac pump wear out. hope this helps.