The following notice is from a cautionary tag on a transmission 
recently put into a '90 Vanagon at the local dealership.  I'll type 
it verbaitum and let y'all thrash it around as to what it means.

"CAUTION! This trans should be filled with 75 or 80 weight SYNTHETIC 
GL-4 rated OIL.  We recommend Redline MT-90, or VW synthetic ( p.n. 
G005 000); this is what the factory uses.

If you do not want to spend the money for synthetic, a straight GL-4 
oil, 75W or 80W, must be used, NOT GL-5, NOT GL-6, NOT GL-3*4*5.  Use 
of any oil other than a straight GL-4 voids the warranty on the 
synchronizers!  GL-4 oil is available from Pennzoil, Valvoline, and 
many other manufacturers.  Do not be talked out of GL-4 by your local 
supplier who may not have it!  VW & Audi synchros were desinged for 
GL-4 oil; anything but GL-4 oil will cause hard shifting and possible 
damage to unit.  Really!  Trust us on this one.

This unit holds 6.4 pints of oil!

Trans # 15518
Type: 83-up

German Transaxle of America, Inc.
63120 Nels Anderson Rd
Bend, OR 97701
503/382-7723
800/892-4327"

***end of quote***