I usually use a sealant on o-rings anyway ..
like the large one that seals the two part of the auto trans ..
I personally would not put one in dry, new or used.
what I do fine with usually is an appropiate amount of a good sealant.
Toyota sells a red one just for sealing ATF.

I think o-ring sealing is a little weird. Since the distance that the
o-ring is compressed is fixed..
you slide the parts together ..the o-ring gets compressed just right ..
and eventually that's not enough compression. Whether in wate-pump
o-rings orwhatever .
That's why I often use a sealant too.

On 4/12/2013 7:37 AM, Richard Koller 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
>