Brad Penn makes a gear oil that sounds like it's perfect for our transaxles. It's called "Multi-Purpose 'Classic' GL-4 SAE 80W-90 Gear Oil". Here's the description: The SAE 80W-90 is specially blended using high quality PENN-GRADE® 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.
That being said, POCA President Les Gray says he's tried them all and Redline 75W90 NS (synthetic) is the best he's ever used in a ZF.
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