Many modern bearings are available in 3 series: open, shielded and sealed - otherwise identical.
When rebuilding my Chev transmission I chose to go the open route, either by using an open bearing or removing the seal from one bearing. I'm not qualified as an engineer to have a technical basis for this but felt that since it had taken 60+ years to develop a bit more roughness than I was willing to tolerate I didn't see a problem with using an open bearing again as I won't be needing the truck in another 60 years.
One other thing to consider is whether any of the seals on input or output shafts need a bit of oil through the bearing to help them slip on the shaft as running dry might cause wear.
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