Rear-end seal?

I have a leak coming from my rear-end. My first thought was the cover, but everything is dry. Seems to be coming up around the u-joint/yoke area. It's a minor leak but im worried it will worsen. I had new gears installed over the summer with a new installation kit (seals, bearings, etc) included. I am thinking maybe he rushed the process. Becuase it never leaked before. From what I understand there is a seal of some sort up in that area. So my question is with the driveshaft and u-joint, etc, off can the seal be replaced? It's a 8 1/4 out of my '74 Duster. I hope it's an easy fix. Thats all I can think of where the leak is coming from. Has anyone here had a similar problem. All info is appreciated.

Thanks