Not sure here which grommets the OP is talking about. Maybe he's talking cowl drain grommets ? If those get plugged, water enters the cabin air filter area of firewall.
Everything below relates to water entering COWL CHANNEL (as shown in tech illustrations). We want to make sure no water enters this area....and into cabin of car from this area.
I'm talking here about 1st, cowl grommets base of windshield. Those should be checked...if they leak, can be resealed, outer edges with urethane sealer. You do not have to replace them as Ford states to do, as they cost over $5. each and there are 5 on each side of cowl, ten total. Once we're sure they are not leaking, next to check:
If not the grommets in cowl, it's often, 2nd, the 'FORWARD PINCH WELD' area which needs to be resealed with urethane sealer...both horizontal (across cowl lip) and vertical areas (just below hood hinge) passenger side of car. Your intent here is to keep water out of the 'COWL CHANNEL'.
Best to remove passenger side black plastic 'COWL PANEL GRILLE' to easily access this area of cowl.
Urethane Sealer from Home Improvement store is cheap and works fine...about $5. a tube plus a cheap caulking gun.