A bunch of PC7. (At Lowes, Home Depot)
It is the 2-part epoxy paste that you mix like play dough.
I would clean the area with rubbing alcohol then when it is dry I would make sure the PC7 is in the hole and a liberal amount around the hole on the outside then To insure it sticks and stays put I would screw an aluminum (Flashing) over the top of it.
It takes all night for this stuff to get hard.