PEH will yell loudly but I agree that it's best to replace all 3 in one fell swoop. If the ones on your car don't have the metal heat shields, it'd be worthwhile to get those as well.

Also, especially since you'll have to pay shipping, it'd probably be worthwhile to get an extra set or two...maybe they're different on the 616, but on the 617, they go somewhat regularly... There are some on here who devised a different air intake to eliminate these parts (and others), due to the issues on the 617 (they go onto a bracket, and the bracket breaks often). Take a look at a thread called "Air Cleaner Mod", started by Dieselhead...it's an older thread, but was recently brought up to the top, so it's probably within the last 5 pages.

Hope that helps some...good luck!