You sort of answered your own question...Easier shifting, cooler
running, increased gear life (though increased tranny life might be
debatable.)  These are worthwhile to some Vanagon peeps.
     In the Grand Scheme of Life....it is probably  inconsequential if you
choose to fill your old VW trans. with mundane gear oil...I am sure there
are plenty of Vanagons out there that nobody has ever even thought about
what the heck IS a transmission, let alone  what might be the best oil to
put in there, and those Vanagons still go along the road OK.
     I have a 5sp manual in my Van, which seems to be an uncommon option.
I choose to give that the best lubrication I can.  I like how quiet and
smooth that Swepco sounds in  there.  I don't find it too difficult to
source Swepco every couple of years to change it out.   I re-use the
'take-out' oil on motorcycle chains...Redline is too thin for that.
  Don Hanson

On Wed, Aug 29, 2012 at 6:00 AM, Tom Carchrae <tom@carchrae.net> wrote:

> I have to ask just how bad is it to use the much more commonly available
> SAE 80W-90 in there?  Or in other words, what is the benefit of these
> harder-to-find oils?
>
> Easier shifting, ok, got that.  Cooler temperatures?  Not clear if there is
> any benefit from these alternatives - or is there?  Will they make the
> transmission last another 200k?  Should I throw the giant jug of 80W-90
> away or use it to flush the transmission?
>
> Mostly I'm interested in knowing why this is a big deal.  It certainly
> seems important to some - I just want in on why.  Is it just you want the
> best of the best, or is it really that the common oil is crap.  What do I
> get from better oil?
>
> Thanks for any illumination.
>
> Tom
>