Leaking Driveshaft...HELP!!!

In the back of the driveshaft slip yoke (see pic above) is a welch plug - kind of like a frost plug. They can, and do, come loose and can leak. Another possibility is as follows - '65 only cars had a vent hole drilled in the middle as mentioned above. This is because 65 was the first year of the slip yoke, and there was, that year only, an internal seal to prevent trans fluid getting into the yoke splines, as the yoke splines were, again that year only, grease lubricated. If yours happens to be a hold over from 65 and has that vent hole, the internal seal in the transmission is finished, allowing trans fluid into the splines and out the vent hole. The output seal, looks to me to be fine, it appears to be coming from the center of the yoke.