Is this why transmission fluid is leaking from my yoke?

[chevymotocross]

I have an 87 2wd with the 700r4. Whenever I park the truck on a hill, I get a massive leak out of the weep hole on the driveshaft yoke. I found on 73-87.com, the reason why this happens and how to fix it (http://www.73-87.com/7387garage/drivetrain/yokeleak.htm). I pulled the tailshaft off, and I did not find the cup which includes the o-ring at fault. I believe this is the reason why it's leaking. I remember the previous owner saying the transmission was overhauled or replaced, can't quite remember. This could be why. So I'm assuming it is suppose to have this according to 73-87.com? Where can I find this cup? I already have the o-ring.

The cup with o-ring which I guess I should have

My assembly, as you can see, no cup: