Not I. I go by spec in the manual and use no additives. It ranges from cheap conventional 10w-40 Mobil oil to synthetic 5w-30 Mobil 1.
As for the valve seals, it would suck if they were leaking even in brand new engines, as some people reported back in the day.
I have a damaged engine with 190k miles. I'll try to poke around the heads to see what those guides & seals look like.