Senza,

The gaskets are re-usable to a point. If your using stock exhaust, or exhaust that has a flange that also uses the same donut gasket, you can reuse it until it is just so compressed it doesn't seal anymore.

Some people will put a little high temp RTV between the gasket and the pipe/flange to get a little more seal.

If you are using an after market pipes, that use a flange so the pipes slip on, and are held in place by springs, then you will also want to add a bead of RTV when the pipe slips onto the flange as well. Put a bead down,and let it setup for a day so it's good and rubbery. and the RTV just doesn't squeeze out while it's still wet.

Thanks,
_________________
Charles Gallant