The ESPCOR manual is old enough it lists 10-W-30 for both transmission and 3 PH hydraulics.  I know the tranny was later changed to standard hypoid, but what about the hydraulics?  By the "smell test", my hydraulic reservoir also is filled with hypoid and not motor or hydraulic oil.  Is this correct?

As a general question, a lot of the '60s hydraulic systems call for ATF Type A.  I know all follow-on ATF is supposed to be compatible with earlier versions, so Mercon-Dexron is OK for these applications.  But I have also been told "universal hydraulic" (10/20) fluid is an appropriate replacement (and I've seen tractors with this replacement).  I know the reverse is not necessarily true as the ATF can foam in this type of application.  So what's the straight scoop (in case I run into this in the future)?