That's million dollar question. Remember there are two fluids. (hypoid grease & hyd. fluid) The hyd. fluid is in a sealed system and I have not been able to find out if there is a change / flush needed and if so, how, and when? The hypoid grease I would think would be changed at the same interval as with a standard diff.I don't see anything in the owners manual about the service interval. I'd imagine 30-60k miles we would need to change the fluid. Did I miss it somewhere? Does anyone know what it is?