Good advice, Chris - that is what I did in the end. I must say, it was a far easier job than with Goldtecs, the only other wheels where I've replaced cartridge bearings.
Still, these wheels were only ever a stop-gap, and I've had them three years now, they were second hand then, the rim is feeling a bit concave, and - importantly - I'd like the rear to be silver to match the SON on the front. S'pose I'll run this one into the ground first, though.