I took the rear wheel off my bike (80s raleigh with modern wheels, used for short journeys mostly) today, and noticed some uneveness in the rear axle. Disassembled to find slight pitting inside on the drive side:
(apparent swarf inside is probably just reflection off residual grease).
(sorry that's not too clear: there are two parallel scratches forming an oval around the ball detectable with a fingernail).
I initially thought some rubbish had made it into the grease and disassembled to regrease and rebuild. It ran a bit 'gritty', but made about the same number of revolutions as the front wheel. I have another problem with the casette (think it's shifted off square) so I'll be working on it anyhow.
Bearings were packed with grease; this is after cleaning. There was no sign of water ingress or rust.
Is this kind of damage 'normal'? i.e. should I be looking for causes other than riding? (The hubs are about 7 years old and the bike has been overladen with bags a fair few times when it was my only transport.) Can I just rebuild with new balls, or do I need a new rh cone as well? I'd really rather not replace the hub: I've never rebuilt a wheel.