Which Yoke and leak questions

65 only (first year of the slip yoke), and possibly some early '66 cars had an internal seal in the trans to keep the trans fluid out of the slip yoke splines, it ran on the smooth machined inner diameter of the slip yoke. As stated above these cars also had a vent hole in the Welch plug in the center of the yoke directly ahead of the u joint, and grease packed splines. This is fact for automatic cars and likely for standards. It is possible this internal seal was left out of your trans and you are now leaking from the vent hole.

Fixing it would look like disassembling the trans to replace the seal, or sealing the vent hole and allowing the splines to get lubed by trans fluid.