RE: about bearings
Greg,
After viewing the NSK material, I conclude 2RS bearings have contact seals, which obviously seal much better that non-contact seals do.
The RPM (in grease) these bearings are exposed to in model engines, is well within their ability.
For example, the R6-2RS (grease-packed contact-sealed) bearing, is limited to 20,000 RPM, a level most .40-.56 engines that employ this bearing will never reach in practice.
Q-500 and pylon racing variety engines should use the shielded type bearing R6-Z (36,000 RPM limit)...
The fact that even contact sealed bearings will leak a part of the grease, following long durations of high RPM/high temperature running, is something I do know...
But even the worst running conditions, a model engine can confront bearings with, are not extreme in bearing terms.
...And the duration of these extremes is always relatively short.
The crankcase rarely exceeds 60ºC (140ºF).
Even when a sealed bearing does leak some grease, it will still retain a sufficient amount of it inside, to continue running without risk of failure.
And it is very unlikely to ever happen in a model engine.
As long as a contact-sealed bearing seals, it is unlikely to leak any significant amount of either air, or raw fuel.