I'm converting my 74 c15 from manual to power brakes. I purchased a remained Delco moraine vacuum booster supposedly for this year tuck. My manual brakes bolted flat to the break/steering bracket with a rubber grommets where it went through the fire wall. The new vacuum booster stands off on brackets. What seals around the brake pushrod where it goes through the firewall? Am I missing a part? Looking at something wrong?