CBF Wheel Bearings

My Honda CBF250's wheel bearings are not proving very durable. In the last year I've replaced the sprocket carrier bearing & a front wheel bearing. Now a rear wheel bearing has gone (at 30,000 miles) I installed a spare bearing I had to keep me on the road and have ordered a few new ones to replace the originals that remain on the bike. The bearings (should you wish to avoid them) are made by NSK, a Japanese company, who manufacture across the world. I've ordered SKF bearings.

Strangely this paste and little balls seems to be what's left of the bearing grease seal.