Rick, these seals are available from Germany directly.  I thought I had one
on the shelf but I guess I am currently out.  You can buy reseal kits
010398007B.
I believe they come with the o-rings you have been searching for plus some
other seals you are going to need before everything is said and done.  I
have them available for immediately shipment if you want to order it.  The
alternative is waiting at least two weeks for one seal to come from Germany.
Let me know if I can help you out.

Ken Wilford
John 3:16
www.vanagain.com

On Fri, Apr 12, 2013 at 10:37 AM, Richard Koller <kollerr@helix.nih.gov>wrote:

> Friday greetings to the List,
>
>                 I'm having trouble locating an O-ring for the diff on a '91
> auto box part # 010 409 259A, dealer says its NLA. Its dimensions are 3 x
> 78
> and I presume that's in mm. Have checked with various venders with no luck
> yet. I did find one at McMaster Carr but not sure if the dimensions for the
> O-ring diameter are inside or outside. Does anyone have a clue,I don't have
> an etka? I'm hoping its an inside diameter since that's what McMaster
> sells.
> Also how critical is it to replace this particular O-ring. I'm going to be
> changing out the 2 pinion seals that reside in a diff housing separating
> the
> two trans fluids and there's 2 O-rings in this assembly that look like they
> should also be replaced. Its one on those that's gone to vanagon heaven.
>
> Thanks
>
> Rick
>