Vin,
Because there was a little play between the collar of my elbow and the pre-filter/grommet, I originaly put an o-ring between the collar of the elbow and the pre-filter for a snugger fit. Recently, I replaced the o-ring with an over-sized black rubber washer, which seems to snug up the elbow/grommet connection nicely and should make for an even better seal than the o-ring and should help reduce stress on the pre-filter opening.
Needed? Who knows, but I can't see how it would hurt.