OK; I can't get a view between the alternator and the bracket and my hands are too big to reach in to the alternator bracket bolts.
However I do have this diagram of the housing showing the gasket and two of the three bolts that hold it to the cylinder head .
If you think you may have removed one of the bolts and see A/F coming out the bolt holes , then thread sealant should do the trick ; however if you don't have A/F coming out through the holes and it looks like the A/F is running down from the housing past the water pump , then replacing and tightening the bolt may not reseal the gasket .