I did not use them when I rebuilt the transmission on my '49 FCUB. I really don't know why that bearing is shielded....seems you would want the bearing lubed as much as possible. Maybe someone else has a better answer.
I think the original bearing had a special hole that had to be at the top so lubrication could come from the gravity gallery. They're often installed with the wrong orientation, so the bearing is more likely to fail.
Whoever worked on my '51 last had a unique solution to the noise from that bearing... leave it out. I don't know how successful it was because I never ran the tractor before I rebuilt it, but I'm sure it wasn't noisy. That's why I now try to at least run a tractor before doing any serious work to it.