From what I can piece together for the Stan's 3.30 hub, you have two 6802/61802 ball bearings in the hub, plus two 6902/61902 bearings inside the rotor body. The latter are no doubt up to the job, but taken together with those little hub bearings it seems very underspecified for a hub that goes mountain biking, where you have all sorts of horrible forces going through the hub and into the axle. Are you hard on your equipment generally?
I think the main problem is that the 61802 is only rated to 1.9kN dynamically, and 1.1kN statically (and that's a good SKF spec).
Compare it with the Hope Bulb of yesteryear, a hub that while a touch heavy was just about bombproof. The Bulb had two 61902 ball bearings in the rotor body (for reference, a 61902 has a load rating over twice that of a 61802). In the hub shell drive side, the Bulb used a 6002 supporting the ratchet assembly (rated three times that of a 61802) and 6001 at the non-drive side (rated two and a half times that of a 61802). The Hope XC of the time simply used four 6001 ball bearings throughout.
Normally I would say replace all of the bearings with SKF, and hang the cost, but on balance I think might look for a stronger hub.
