check
Daniel Stern Lighting Consultancy and Supply for some info about bulbs.
I just installed some Narva +50 in our 03 and they are nice. Seem brighter than stock - hope they last.
you might also pull connectors apart, maybe spray them with electronic cleaner, reconnect them and smear a little dielectric grease around the mating surface of the plastic connector to help keep moisture out. maybe tighten-up/refresh ground connections too.
Those Narva bulbs are great in H3. I ran them for fog in my SVX, along with the Toshiba HIR1 bulbs for low beams

At
Currently running Hella High Performance Xenon blue 100w/80w bulbs in the OB. Best bang for the buck honestly, $30 with a 1 year warranty and a whiter light. With the stock 9006 fog bulbs and these on low beam, I get people flashing me to turn my lights down occasionally

My next step is to install some Hella FF500 driving lamps in the stock fog locale, or if possible fab/alter a light bar on the top of the front bumper and mount there, to install FF500 fogs in stock location
To the OP: You have a PM. I may be able to help you out with your problem. Auto lighting is one of my niche's, and I'm good friends with the guys that run one of the largest East coast warehousing distributors for Hella, and I'm 99% certain they'd be willing to offer a club discount to forum members who order.. Most times the lights fade due to oxidation on the outer lenses. But the bulbs themselves can become weak over time, usually towards the end of their life. Which is no surprise considering what extremes the bulbs endure.
One more thing to try if you do what Tex said above regarding dielectric grease, etc. is to take some sand paper to the terminals on the back of the bulb. These should be 9003/HB2, similar to my 97. DO NOT touch the glass on the bulb though, and if you do happen to accidentally touch it, make sure to wipe the glass off thoroughly with rubbing alcohol before reinstalling.