Originally posted by Flyboy Dave
....periodically flood the crankcase with oil through the
breather nipple....and remove the valve cover and oil the
rockers as well. Thin some oil a little bit, and run it down
the pushrod tubes, and flood the cambox as well.
After you run the 4-strokes for awhile, you will find out that
they really don't lube from the "blow-by" worth a hoot. In fact
no oil gets to the cambox and rockers at all. They rely on the
hardness of the metal surfaces to make them last. 
Dave. 
I can't argue about other brands or models but I take exception to this when it comes to the OS Surpass .91's (I & II). I've run a number of these for about five years now and usually check the engines at least once or twice during the season for valve clearance, cam and cam follower wear, etc. The parts always show a reasonable amount of lubrication when I pull the covers and I never see "dry" parts. The valve clearance doesn't seem to change at all indicating no wear in the valve train.
On the other hand, I don't run my engines leaned for every last RPM either so there's always a slight smoke trail. I also use fuel that has at least 18% oil in it (but no castor), as recommended by OS.
I really doubt that the better manufacturers (OS, YS, etc.) design their engines without ensuring proper lubrication to all the parts that need it. That to me would seem to be asking for it, liability-wise.