Got a set of Deore hubbed 700c disc wheels that are 5+ years old, with at least 10,000 miles on them. Free hub had started to feel rough so decided to replace it. Opened the hub to find it still full of grease, bearings pretty much good as new and I reckon I could have cleaned up the free hub and got a few more miles from it, but as I had a new one I decided to put it on.
I'd never opened one up before either, always been a bit "scared" of cup and cone hubs but it was a piece of piss to do. Happy days