What I have been told by my rebuilder is that these units typically fail because the seal between the diff and tranny goes out, allowing the gear oil and ATF to mix. This will eventually take out the diff, and quickly gums up the valve body.  

This type of behavior could be from thick gear oil in the tranny.  Unfortunately, a complete rebuild is necessary, including the torque converter, since it's the only way to get the cross contaminated fluids out. 

The seal seems to last about 25 years, regardless of mileage, according to this fellow.  

Stuart

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Larry Alofs
Sent: Tuesday, December 09, 2014 8:55 AM
To: vanagon@GERRY.VANAGON.COM
Subject: AT question

Volks,
  I have been working on a rather nice '91 GL, soon to be for sale.  The last issue is the transmission.  If the van has not been driven for a couple of days, the transmission is reluctant to get going at first.  When I shift into drive or reverse I can feel it engage, but the vehicle moves very little until I run it at 2500 rpm or so for about 30 seconds.
  Once it starts to pull, it works fine for the rest of the day, shifting smoothly at appropriate speeds, etc.
I have tried a dose of Seafoam followed by a fluid and screen change.  This approach has worked well for me on other types of vehicles with the same problem, but not this time.

Can anyone offer a considered opinion about the cause of this problem?
Will I have to go into the trans itself, or is there some hope of a remedy by changing the torque convertor or governor or cleaning the valve body?

Larry A.
W. Michigan