IP 370 Holding Tank Barb Fitting.

Our 2004 IP 370 aluminum holding tank hose barb (where the 1.5 inch sanitation house attaches to the tank) has started to leak. As I took it off I noticed that the aluminum has bent and corroded. Looks like there are a number of screws that are fitted to the side of that will need to be removed. Two questions, anybody know what sealant they used and where can this be purchased or will I need to have one custom fabricated? Thanks i advance.

If any of you had experience with this, how difficult was it to get the screws out. Thanks again.  The tank is fiberglass but the hose fitting is aluminum.