When you change the differential fluid in your vehicle(s), do you remove the diff. cover, clean the inside of the diff. and all the mating surfaces, and apply new gasket maker? Or do you just pump out the old fluid, pump in the new and get on with life?

I've always done it the long way, but I need to do both the front and back differentials on my truck this weekend and don't have a lot of time to get it done, so I am contemplating just pumping out the old fluid. Other than not being able to visually inspect the internal gears, I guess there's not a huge downside to this approach, and that's probably what a shop would do anyway. But I'm curious what the Lounge has to say.