I recently changed my transmission and rear differential oil at 23711 miles over to Amsoil GL4 ( http://www.amsoil.com/products...00967 ) , at the HPDE I was at I could hear transmission noise after a run and decided it might be beneficial to change even though it was a "lifetime" item.
EDIT: If doing this again, I would use the same GL4 (Manual Transmission & Transaxle Gear Lube 75W-90, Product Code: MTGQT-EA) I used for the trans and get GL5 (Severe Gear 75W-90, Product Code: SVGQT-EA) for the rear differential. Amsoil is great stuff but their product guide is sometimes lacking, and GL5 contains additional additives that provide better lubrication for the rear diff.
I will let you draw you own conclusions from the below oil analysis results:
[EDIT] Changing Your Transmission and/or Rear Differential Fluid 101
Since there were some requests in this thread I have copied the info from my website to the below DIY.
Basically you use a tool like the one I sourced from MetalNerd to remove the fill and drain bolts:
One end works for the transmission and one end works for the differential. I always like to go for about a 30 minute drive to warm the fluid up and get all of the sludge out <IMG NAME="icon" SRC="https://forums.vwvortex.com/zerofile/5998/halloween_pumpkin3.gif" BORDER="0">
Next, I jack the car at the front jack point high enough to get a jack under the rear jack point on the pinch rail and under the frame at the front (these points are not VW approved, YMMV). No need to remove wheels, I did this for another parallel project.
For the rear differential, remove the fill bolt first and then the drain bolt and drain the old fluid into a suitable container for recycling:
For the transmission, remove the fill bolt first and then the drain bolt and drain the old fluid into a suitable container for recycling:
When all fluid is drained, replace the drain plugs and tighten to spec. You will need a hand pump like the Sta Lube one to fill easily. It takes 1.05 qts for the diff and 2.7 qts for the trans and will start to pour out of the fill hole when capacity is reached, this is your queue to remove the fill tube and replace the fill plug.
NOTE: The VW Oil Check process should be followed, specifically note the requirement to run the engine with the transmission in gear for two minutes before RECHECKING the fluid level for the transmission/front differential. The VW torque spec for both drain and fill bolts for the transmission/front differential is 30 Nm or ~22 lb/ft and for the rear differential is 25 Nm or ~18.5 lb/ft. :
Modified by wrh3 at 1:07 PM 7-5-2009