Header tank issue

Did you look at it with the fuel valve on or off? I had a tiny crack in the copper tubing to the primer. I never smelled fuel when the airplane was sitting with the valve off but I could smell when the valve was on. Also, the primer itself can leak. You should be able to spot blue stains anywhere it leaks.

You might be able to buy some time with a sealer, but it will fail sometime in the not-too-distant future. I messed with it for a couple of years but it slowly got worse.

If you have an older serial number (I can't remember the cutoff, in the 2000s somewhere) it was built with a 5-gallon header tank, which is no longer available new. The only header tank available new is the 6-gallon header tank from Univair, at some crazy price (used to be $3,000). These are welded tanks and are not rebuildable. My airplane was legally converted to use a 6-gallon tank in the 80s, but after 20 years that tank failed. I finally purchased a riveted 5-gallon tank from Vernon Gregory, and we tested it and replace a couple of rivets. It was installed in 2010, and still working fine. I'm sure a tank from Univair would still be fine, too. Regardless, the labor of removing and installing a header tank is huge. Everything under the tank must be removed - for me that was control cables, radio and transponder trays and wiring, control columns, gauges, etc. It requires a lot of work in an uncomfortable position in a tiny space!

Many people have removed a tank and had a licensed shop "rebuild" it by replacing everything but the filler neck...

I hope you can get some time out of your current tank!