Air Cooled 4 sp. - 2.9L (3.2 qt.)
Water Cooled 4 sp. - 2.5L (2.8 qt.)
Diesel 4 sp. - 2.5L (2.9 qt.)
Diesel 5 sp. - 3.4L (3.8 qt.)

VW specifies 80/80W/90 weight with a MIL-L-2105, or API rating of GL-4, but
API GL-5 are now the most advanced gear lubes. It adds an impact additive
to GL-4 to combat gear lash. Caution: There is some controversy about using
GL-5 in transmissions specifying GL-4. Some manufacturers claim they should
not be used, others that they supercede the previous GL-4 spec fluids.

Bla bla bla and bla bla.... another scam from manufacturers.

I use engine oil!!!! in all my Manual Transmission, but don't follow my
example, I like to play with fire...

Ben
http://www3.sympatico.ca/huotx/engine1.htm