Vent hole in yoke started sporadic leaking. Why?

Same yoke and output shaft for about 1000 miles on my rebuilt C6. Yoke has the plug with a small dimple in the middle and a dinky hole in the center. Had zero leaks until about a week ago. Came out in the morning and had an oil zit about 8" round under the yoke,probably an ounce or two. Used the car a few times after that and it didn't leak. Last time out it left a zit again. It's coming out the yoke vent hole but my question is why? Nothing changed,I didn't add oil. I don't want to plug the hole if I'm missing the real problem and just eliminating the symptom. Is there a failed inner seal or something that would cause the yoke to load up with more oil than normal. The main vent on the trans body is operational. The yoke and output shaft are both fully splined so there is no missing spline to release oil and prevent a hydro lock if I plug the existing hole. Any thoughts?

Some C6's have a rubber seal on the output shaft . With that vent hole it would need to be in good condition

I just figured out where the leak was last night so I put a call in to the friend that did the rebuild. Hopefully I hear back this week.

You called it. Inner seal. Spoke to my trans guy. My C6 is from a Lincoln and I know it has an unusual output shaft/tail housing/trans mount. I guess there is a specific yoke (not the one I have) for this unit that is longer and has a non-splined area that slips over an O-ring on the output shaft to seal the splines. Still not sure why it started drooling out of the blue but I tapped the vent hole for a tiny machine screw with a bit of goo and driveshaft is going back in. I wouldn't call the splines in the yoke or on the output shaft from 1972 "factory fresh" so there's some clearance for oil to move between the two and not hydro-lock.