I have used a lot of 7200 series bearings. They are mostly a thrust bearing, one side is cup, one side is cone. So how you put them is important. I've seen millwrights put them in backwards. Sometimes it's pretty easy to look good. On one common use ,we used two, back to front. We never had any 7200 with seals. Your top bearing should have a seal to close in the cavity . I wouldn't worry about the bottom. But I would use a super premium grease like Mobil 101. A problem that is in some designs the preload is governed by the dimensions of the nut and housing. When either wears or is over tightened and hammers out, the preload is reduced. I've seen that slop more than a few times.