Unknown history on mine so I changed all driveline fluids when I got it at indicated 60,000 miles. Rear diff oil looked a little silvery/cloudy, but I have nothing against which I can compare. (Any pics to compare against welcome)
What I did was use a decent semi-synthetic as a flush for the first year.
I now have some of this ready to change in the summer.
Motorsport CRX 75w90 NT+ - Millers Oils
It's been interesting seeing how long I can leave the good stuff in for.