New gears - what kind of oil should I use?

I have a '96 XJ with a Dana 30 front and a Chrysler 8.25 in the rear.

About 5k miles ago I had the axels regeared to 4:56. The front Dana 30 has an ARB air locker, and the 8.25 rear has a limited slip Track-lok.

I sort of feel bad for waiting so long to service the differentials. How much metal should I expect to find? Anyone think I did any real damage by waiting so long to service them?

What is the best weight of synthetic gear oil for me to use? Temps are 20-30 in the winter, 100 in the summer.

Thanks

Time will only tell, you should have changed the oil at 500 miles, shame on you.

After brake-in I went to 75-90 Mobil 1 Synthetic. Don't forget the friction modifier for the rear limited slip.

Greg

I use Valvoline 75 90 synthetic.

first and formost, check with the guy that installed your gears. That being said, take your pic. whatever is the best deal when you go buy oil. for synth I suggest either Royal Purple, Redline, or Amsoil. but you could easily run the cheap $5/gal 75-90 off the shelf and be fine with it.
do run a 75-90 or 80-90 and not a -140wt oil. you don't need it. and yes, do use the friction modifier.

Red Line Gear Oils, with the exception of the 75W90NS, and 75W140NS, already contain friction modifier required for operation in limited-slip differentials. Additional additive is not required.