I also did both of my diffs at 30k. Rear was black front still looked clean. I used a suction pump for the rear to pull the old oil out, yes I know you can’t get all of it but I figured at only 30k for the first oil change it would be enough. And I also used Amsoil severe gear to refill it.

 

I did mine at 65, but got spooked from the reports of snapping cover bolts so I just pumped out what I could and put new in. I got most of it that way. Better than nothing. What did come out didn't look too bad. My transfer case was much worse.

 

Do it early, I didn't, carrier bearings are not cheap to be installed lol. A ring and pinion would be worse. Had a howl and serious pitting on my races from water.

 

You're driving fewer miles than me, and I'm not getting my diff fluid hot enough on a regular basis to drive out moisture. You should be operating on an extreme duty service interval. I'm swapping out diff fluid every other year, and it's obvious that it needs to go..