I've had a Shimano R500 wheelset on my winter bike for about 5 or 6 years now and done several thousands of trouble-free miles in the wet and muck, so decided it was high time to give them a bit of tlc.
Axles stripped, cleaned, bearings replaced, regreased, and reassembled, and a spin round the block to check everything is working as it should.
I was really surprised at how good a condition they were still in. The original grease was still green coloured and not the usual grey gungy stuff you'd expext to find, and there was minimal wear on the ball races. Amazing really for such a budget-priced set of wheels.