Use clear RTV silicone adhesive to seal the area that is leaking, where the lens is glued to the body. Better yet, dismantle the lens from the body, remove all the old sealant, clean everything inside the headlamp with alcohol and then reassemble the lens onto the body with clear RTV silicone adhesive. There are numerous online videos showing how this cam be done. Here's one I like.
https://www.youtube.com/watch?v=sEiSQXavr7w
Your glass lens headlamp is worth salvaging by repairing the leak if you can. I'm not a fan of the plastic lenses now installed on all types of vehicles or offered as aftermarket replacements. The original headlamp and all later revisions from Infinity have been discontinued. If you can't find an original replacement from a salvage yard, then repairing what you have is a good option. If you do find an aftermarket headlamp that fits, you will likely need to get both headlamps replaced, if you want them to match, because the look of an aftermarket product will not match the look of the original. There were a number of original headlamps for the '98 Pathfinder. The best way to find the original Infinity part number is to lookup the part using your VIN number. You can then use this original part number to find a replacement aftermarket headlamp that should fit. However, like I said, you will need to get both headlamps replaced if you want the look of the headlamps to match. If you don't care about the look, be advised, the lighting illumination of an original and an aftermarket headlamp will look different as well.