Hi I just bought my first fishing boat it is an old boat 1995.  It has a metal livewell and I was looking to seal a leak somewhere inside it that I can't find.  Was wondering what type of sealants I could use inside of it.  Thanks

Google "gluvit".  It's an epoxy that can be brushed on or rolled on.  Coat the entire surface of the live well, sides and bottoms.  It will seal all small cracks and crevices.  It is also used to seal mobile homes at the seams to stop leaks.  It remains flexible.

Make sure the surfaces of the live well are free from dirt, grime, grease, etc.  Scuff with sandpaper to get a good bond.  It's an epoxy, so it bonds well to almost any clean surface.

Flex Seal and truck bed liner would be alternatives, but @Fishing Rhino's suggestion is probably the best option.