I happened across THIS info. on the Novak site:
http://www.novak-adapt.com/knowledge/transfer-cases/np231
Particularly, THIS excerpt:
"ATF is the factory recommended fluid, however many individuals have chosen to run a straight 30 weight oil or 5W30 in a mineral or synthetic. Our experiences with these and those reported to us by our customers indicate positive results in noise reduction and wear resistance."
http://www.novak-adapt.com/knowledge/transfer-cases/np231
Particularly, THIS excerpt:
"ATF is the factory recommended fluid, however many individuals have chosen to run a straight 30 weight oil or 5W30 in a mineral or synthetic. Our experiences with these and those reported to us by our customers indicate positive results in noise reduction and wear resistance."