John,  I used some greaseless silicon spray on my secondary valve
seats.  I think this is a good idea for three reasons:

1) It will keep the valve face from tarnishing;
2) It will reduce the chances of the valve sticking to the seat;
3) It will ensure a proper seal with minimal leakage.

I set up a simple jig to spray the valve seats by drilling a hole the
diameter of the bowl of the seat in a piece of wood.  You simply place
the jig over the valve seat when you're spraying, and none of the
sealer gets on the rim.

Cheers,
Michael Gordon, from Toronto, Canada