Stephen,
If you're looking for a good bearing at a reasonable price, I would recommend these in the link below.
http://www.vxb.com/page/bearings/PROD/kit7594_1They held up well for us over the year but, we were replacing them 2-3 times per season due to the reasons you cited in your post.
What solved our problem was purchasing a new set of urethane roller from Golfco International in Seattle. These rollers are undoubtedly the most well constructed and easily rebuildable roller I have ever seen. They run about $260 per roller with shipping and will last MUCH longer than the OEM style roller. We have been able to run these rollers nearly two seasons without changing bearings.
http://www.golfcointl.com/images/Golfco ... 12K15w.pdfhttp://www.golfcointl.com/designofgolfcorollers.htmlIf you have a Precision USA catalog, in the roller section they have a nice cutaway photo of the roller and how the bearing is housed in the shaft. While the upfront cost is significant, the ease of maintenance, durability, and longevity are definitely worth it in my opinion. Martin Doyle is the owner of the company and is great to deal with as well.
I hope this helps.