I checked a couple more of my OS Max-S engines. They all have a .005" steel washer. I just didn't get one in the engine I rescued last week...but it also had a Home Despot flat washer under the prop nut, too.
But,....neither the OS instruction sheet for the Max-S .30R/C nor the Max-S .35 Stunt lists a shaft spacer (friction washer, anti-wear washer, precision shaft spacer, etc.) in their respective parts lists. The .35 instruction sheet has an exploded view which does not show a washer either.
The fate of the world is obviously not hanging on this detail, but it was interesting to see if they came that way, or if there have been gnomes at work throughout the land, placing precision shaft spacers on all OS products not so endowed by the factory. And if so, are those skilled little guys available at reasonable rates to replace worn piston/liner setups....
Dave