It is OK to mix some dino oil and synthetic....can't get it all out
during a change anyway.
Best to change it when its warm..more drains out faster
Remove the fill plug before the drain plug....gotta get new oil back in
once you drained the old stuff out...think about it...
The most important thing to do is change it once in a while...basic
maintenance does wonders for longevity...
GL4 is what Redlne oil is...MT-90 is what they recomend for Vanagon
transmissions...
GL-5 is what's supposed to go in the front diff (syncro) cause there are
no syncro's there
Any good quality synthetic will work better than the plain old 90 wt
stuff
Redline has been proven to ME to be the best overall performer esp when
shifting cold is a problem
You can go to redlineoils.com and buy from them or I stock several cases
so can also sell it to you.
As I understand it...MT 90 is for Hypoid diferentials (gears at a 90
degree angle to each other) such as your Vanagons...MTL is a lighter oil
and is for the Jetta style tranny's which use straight cut Ring/Pinion
gears...
Any degredation of syncro's from using the wrong oil takes many many
miles....its not something that happens quickly
Feel free to holler with any wierd questions....
Daryl of AA Transaxle
Duvall, WA.(Seattle area)
(425) 788-4070
1-877-377-0773 toll free
http://www.aatransaxle.com (web site)