I'm pretty sure P.T. Barnum originated the "use lead additive" advice. It's a good way to transfer money from gullible people's pockets to the people who sell that stuff. Unless you're running some sort of super-dry fuel like LP gas of CNG, there's no reason whatsoever to worry about having hardened exhaust valve seats. Your engine is in a lot more danger from an incorrectly-installed seat coming adrift and wrecking it than any problems that might happen with erosion of the original seats.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!