We used to use a moly disulphide grease on open valve gear (on a 1920's car). Norton SV valve guides are probably an ideal application I should have thought. Messy stuff...
I have used both molybdenum grease and airgun grease. But not for long.
Having the idea that its all gone through the exhaust before you have left your home street I just stopped greasing alltogether.
Have not had any problem for over 10.000 km.
OK, I may not have the best of compression but I also seldom push the bike to its limits.
This is not a call to stop greasing, only to show that what you do, it is not necessarily going to be wrong, and these MC's can take a hell of abuse and still run happily.