Found my water leak

Ok so I have finally found my water leak. I thought it was coming from the air box so I carefully cleaned the relatively clean cowl section, not a thing in there now, but I still have a leak. The leak is actually coming in around the heater inlet tube. Kind of hard to explain. On each side of the car there is an air box. That air box has what appears to be about a 4 or 5 inch diameter tube that goes up to the cowl. The water runs down the outside of that tube and pools on the floor below. There appears to be a sealant of some sort on the inside but it is cracked. Can I just use something like silicon sealant or is there something special?