Here is what I got either on the Atlas website or they emailed to me. BTW, I use the Torco product. Hope it helps:
This unit is shipped Dry. Before operating your Atlas, please fill with the recommended gear
lubricant (Torco MTF). If you are unable to find this lubricant, one of the following synthetic oils can be substituted for the Torco brand: Castrol Syntec 5w-50, Valvoline 20w-50 or Mobil 1 Synthetic 15w-50. We have found these synthetic lubricants to work well in the Atlas.
The recommended oil capacity is 2 quarts in the Atlas 2 speed and 2-1/2 quarts for the
Atlas 4 speed transfer case. The Atlas does not offer any type of ‘weep hole’ to verify
the oil level. Therefore, we have supplied your unit with a site tube to aid in
determining the correct fluid level. Once the required two quarts are put into the
Atlas, we recommend marking the oil level on the site tube. We like to use a small
zip tie as a oil level marking device. Note: When the Atlas is overfilled with more
than the recommended levels, it will cause the unit to vent the extra oil out the
Before lowering your vehicle, fill your Atlas with the Torco oil provided. By using a hand pump, connect the hose end to the upper fitting of the site tube to fill the Atlas to the recommended oil level. Once this is completed, re-secure the upper site tube fitting to the Atlas. If you are unable to find this oil brand locally, we offer it under P/N 303200, or you can use one of the following synthetic oils as a substitute: Castrol Syntec 5w-50, Valvoline 20w-50 or Mobil 1 Synthetic 15w-50.