Was there any firewall modifications or new sheet metal work done? Pictures always help too. Most of those grommets have a groove that accepts the firewall. I had the opposite problem, as my grommet wouldn't stay in place. it would poke through all the time. Maybe try warming it up a little? Make it really pliable, then it should go in. You can put in boiling water or a heat gun. Just don't melt it.
