[supertrooper]

Looks like this is what I am looking for. My dad did some more checking found someone that also recommends the GL-4. Most is GL-5 and not what the transmission wants.

Here is a quote from Penngrade oil.."PENNGRADE 1® CLASSIC GL-4 GEAR OIL SAE 80W-90
PennGrade 1® Multi-Purpose ‘Classic’ Gear Oil GL-4 SAE 80W-90 is a specially blended using high quality premium mineral base stocks and select additive technologies. It is designed to be used with “yellow” metallurgy (brass, bronze, copper) and other ‘soft’ metals used in synchronizers, bushings, thrust washers and other components typically found in classic manual transmissions and transaxles. In applications specifying API GL-4 quality lubricants, use of API GL-5 lubricants with higher extreme pressure additive activity/concentration can damage these ‘soft’ metal components."

This makes perfect sense and I am confident now to replace the fluid with a GL-4.

Thanks!