[blykins]

You'll have to determine if it's leaking from the gasket between the pump/timing cover, the gasket between the backing plate/water pump, or leaking from the weep hole in the water pump.

Any water pump gasket will work, just get one from Napa, Autozone, Advance, etc.

If your expansion tank bolts to the intake like a thermostat housing, you just need a regular thermostat housing gasket.

As for the gaskets, I use an extremely thin coat of black RTV on both sides.