That's strange. The endbell bearing doesn't have to deal with nearly as much load as the...bearing on the other end, I can't remember the name off-hand.
I use Boca Yellow Seal ceramic bearings in all my motors. However, if I were going to run in really nasty conditions on a regular basis, I would consider replacing one or both bearings with bushings, because they're easier to clean. You could replace just the endbell bearing with a bushing without suffering any loss of performance or extra heat buildup, because the endbell bearing has almost no load on it.
I'm really asking this question, not trying to generate a fight or anything.
Fyrstormer, why don't you just buy the brushed motors and use them instead of being all the time changing their components and modding them? Maybe it's just for fun, cause it looks fun. But if it is not for that reason, why do you do it? There are lots of brushed motors that are hi quelity out of the box.