i found the internal o-ring, the one retained by the hair clip snap ring, and also the large o-ring that fits on the outside of the speedometer gear housing.
as to the one on the speedometer cable, well, i'm still looking. [for a speedometer cable to see what that o-ring looks like. i know there is one here, just in which "pile-o-stuff" is it in. ]
if you can't source one locally, i'll get it in an envelope for ya..........

There is no seal "on the speedometer cable" on the '66 and later. Outer seal on the adapter is an O ring, inner is a molded lip seal.

I will track one down locally, but thank you for looking 👍

No one said the eguy is cheap, that about 3.00 worth of parts BUT he's providing a service and get paid for doing so

Exactly. I don't mind paying a few extra dollars to get the right parts delivered right to my door, especially with covid. Most auto parts places around here are still on limited hours and nothing is in stock. So I have to drive to at least one store, place the order, and then drive back again to pick the parts up days later (and hope I got the right stuff). I just went through this with buying shocks - one store had fronts but no rears, another store had rears but no fronts. The distance to hit them both was 40 miles and I couldn't do it on the same night because the stores both closed at 6pm. I said the hell with it and bought them through Rock Auto.

I just ordered a set of 5 of the "ATP" #SO13 on Amazon for $4.61 and free shipping. My local stores had their own part number with minimal part description. Since some of you already confirmed the brand and part number, I know I have the right part coming.

Thank you again!!

I had the same problem and fixed it yesterday. I just got my 727 back from being rebuilt and I bought a used housing and gear which came with a new O ring and internal seal which was missing from the transmission. The housing came with a new seal and O-ring and it leaked and ran down the cable. Yesterday I pulled the housing back out and noticed there was no resistance when pushing the gear into the seal so I replaced it with the one the trans shop sent with me out of the rebuild kit. Now I could feel the seal againts the gear and the leak is gone. Some one must be making a seal with the wrong dimensions .

Another thing to look for is any lateral scratches (lateral meaning across) the areas where the seals sit. Bubba likes to use metal picks to remove the seals leaving the scratches behind, check the gear as well although I've never seen one with damage. If you find any and they are not deep, just polish them out leaving a "radial pattern"

you can remove and replace the internal lip seal [o-ring it is NOT ! thanks JK, for pointing out my mistaken nomenclature !] without removing the tiny hair clip retaining ring if you are super careful with the new seal and use very blunt, correctly sized for the job, probes.
just make sure both seals, especially the new one, are lubed up good.

I usually take the seal and retaining spring out, inspect, get the seal started and use a 1/4" deep socket to push it into place. Then start the spring and use the same socket to push it down until it just touches the seal. Be aware that pushing it in too far will distort the seal And yes lot's of lube is good

Thank you everyone! I hope to start on it later this week.

And yes lot's of lube is good....where have I heard this before??? Oh that's right...work

hmmm............

Does this look like the right creature? I was expecting one a little larger for some reason.
Picture too big but it measures about a half an inch in diameter.
Thanks

Dumb question: the cone shape of the seal goes away or toward the housing?
The black one that I pulled had the cone facing outward.

Thanks!

The cone tip / lip faces inward toward the gear. Not outward toward the cable.

Yes, they are that small.

Thanks!
The black seal had the cone facing outward! I marked it with a blue paint marker before I removed it from the housing.

The one on the lower right corner (looks dark brown) is how it should be installed into the housing(bottom side first) from the outside in towards the center of the trans.

The tan one if installed into the housing (bottom side first)as pictured would be backwards.

OR, The recessed side with the lip goes in first towards the center of the transmission Got it ?
then install the clip to just touch the seal holding it in place.

I think TJP did a better job of describing it but I drew a picture. LOL