>Don't know about a 90, but my 86 has two plastic "expansion tanks" which 
are
>connected to the main fuel tank by small vent hoses.  Several years ago one
>of the tanks on mine developed a small crack which left gasoline odors
>everytime I filled it, but I never could see spilled gasoline.  The tanks
>are under the drivers and passenger doors on mine.  I would look at them
>closely before doing anything with the main tank.
>
>Imagine you could repair those tanks with GOOP or some similar adhesive.
>But I got my replacement free from VW under the extended emissions control
>warranty.

I'm not familiar wih "GOOP" adhesive... once saw a "GOOP" shop hand
soap... but I digress.

Several companies make stuff called "Gas Tank Sealant", designed
specifically for cracks in tanks that are continually exposed to
liquid gasoline. Sorry I can't cite specific manufacturers, but I
got some at the FLAPS (Kragen, or Checker for you midwesterners) and
used it on a crack in my '66 Mustang's tank. Have had zero problems
since. It even hardened and sealed on a tank *AS* it was trying to
leak! Better to use it on a tank that's almost empty, of course.

You can make the bond stronger by sanding or scraping the area around
the crack to roughen it up and clean it. Then cover the rough area
with sealant putty, and work putty into a small piece of cloth and
molding it over the crack. The cloth will like triple the strength
of the bond-- old model-plane builder's trick. Works for fiberglass,
too, of course.

 -Steve Maher   smaher@gi.com   '71 VW Transporter