Bob Rooks
Elite Member
The GL spec is an API rating that, among other things, indicates the corrosiveness to yellow metals. And so far as I know, neither UTF or UDT have an AGMA rating, however, Caterpillar Torque Fluid TO-4 does, as does ISO AW 46 and 68 hydraulic oils.
http://www.tribology-abc.com/abc/viscosity.htm
http://www.tribology-abc.com/abc/viscosity.htm