It's as good idea to wipe the dirt off from around the front bearing when it gets dirty and occasionally put a drop of 3-in-1 oil in it and spin the shaft a little to get it to work its way in. Then wipe off the excess oil to keep it from attracting dirt to the bearing. I'm not sure on bearing size but they're quite large, something like 5x16x5 but you'll want to check with calipers before ordering some but you shouldn't need bearing for a very long time.
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