If the oil smells this is a sign water has got into the hub and mixed with the oil, if you ever submerge the hub this can happen, other ways water can enter is by being forced under the seals by a pressure washer or driving in heavy rain on a car rack at speed. As long as you do an oil change as soon as you can after water ingress occurs there is unlikely to be any damage to internal components. If a hub is ridden an excessively long time with contaminated oil it can mean the bearings are starved of oil or the internal clutches start to get corrosion on causing mis shifts.
Dave