Re-fitting petcock back on gas tank?

Just wondered if any of you guys use any gasproof mastic when re-fitting a petcock back on a gas tank. Is a new O ring as supplied with a petcock repair kit usually sufficient on its own.
Tommotbird

Are you talking about the bolt-on style of petcock with the oval o-ring?

If so, I've just relied on the o-ring with out any additional sealer, and it has worked fine.

Usually the o-ring and bolts work just fine, but if youre like me, and a bit paranoid, there is a tube of stuff you can get called "Seal-All" and its pretty much impervious to gasoline. It dries quick though!

Orings work if new, but if for some reason the petcock ever needs to be removed, reusing the old oring will leak every time. For this you can seal with Yamabond #4 or equiv. I rarely replace the ring, just put a little Yamabond on the existing ring and no leaks. The mount bolts with the plastic washers never leak, just the oval ring.

As long as you have a new o-ring you won't need sealant. If you reuse an old o-ring that is deformed it will leak unless you use sealant. I bought a couple extra o-rings while they were avaialble and cheap to avoid the problem in the future. Ed