Output shaft bearing is a ball bearing, not really meant to control "wiggle". Just a support between the rear support and the tailshaft bushing. You can try a bushing, but I lean towards the shaft not being 100% right for a high frequency vehicle speed related "buzz".

Have it checked. BUT at 1:1 in high gear the shaft is spinning at engine speed (or near with an auto) At 80MPH, the shaft is spinning ~4000RPM, maybe, depending on the rear gear. Most shops can't spin them nearly that fast or hold a tight enough tolerance. I would do what I had to do to get it to someone who can do a high speed check and/or balance before tearing the whole car apart.

I've had a shaft that was built with one (or both) end slightly off center, .010-.015 maybe. It would balance up and be OK for awhile, but the buzz would slowly reappear over half a season at 7000+ RPM. Got tired of it, threw it in the scrap, got a new aluminum unit, problem solved. Smooth for years after that. A bad shaft is a time bomb.

Also, in my experience, if the rear bushing gets too loose (high mileage, etc.) it will allow the yoke to move around enough to create an oil leak at that seal. If there is no evidence of the yoke moving beyond what the seal can control (leak), I would look at the shaft. Also, had a shaft out of balance/off center far enough that the yoke was "whipping" or "wallowing" around in the bushing. Evidence of that was a bushing that looked like crap and a smear of bushing material on one side of the yoke surface.