Max,

Because RTV is *not* fuel proof.  As it becomes gas soaked, it expands.
NEVER use RTV on fuel system components. (Or on any other part of your
bus.)

Examples:

Case half sealer - Loctite 515, Gas-ka-cinch or Yamaha Three-bond.
Oil pump - dry
Sump - dry or a dab of wheel bearing grease
Valve covers - 3M Weatherstrip adhesive on the cover side, grease on the
head side
Carb/FI gaskets - dry
Glass gaskets - silicon windshield sealer or roofing tar (wet-patch)
Vanagon fuel tank - new grommets

and so on. If you have questions, look in the Yellow Pages under
Adhesives - Industrial and call the local supplier. They will rarely
steer you wrong. RTV is for building aquariums and sealing storm windows.

Jim

Max Wellhouse wrote:
>
>  However, I accidentally shook loose the breather pipe under
> the gas filler(I was going to pull it anyway to look for foreign objects
> before I put the tire back on), and lo and behold, here's a huge glob of
> clear silicone all but totally constricting the vent hole.  Now when I did
> the Wilfy fix for the crossover pipe, I vaguely remember putting a "dab" of
> rtv to help seal the nipple type gasket, but not THAT much!