350 TH vent hole leak?

[Bob W]

I replaced the shifter shaft seal and I am still getting a leak on that side.  I cleaned everything off, and started looking around with a flashlight and a mirror.  I came across a hole near the top of the transmission case, about 5-8 inches above and slightly forward of the shifter shaft.  It is a vertical hole about 1/4" in diameter and about 1/2" to 3/4" deep which intersects with a horizontal boss which appears to be the same diameter.  The hole is flush with the transmission case, and it is very clean as though it once had something in it, or is clean because fluid has been coming out of it.  
Two questions?
Is there supposed to be something attached/inserted in the hole?
If nothing is supposed to be in the hole, what would all of a sudden cause the transmission to start spitting fluid out from there when it worked fine and wasn't leaking before?
I checked the dipstick (static) and there is still plenty of fluid so it is not as though it is pumping itself dry through this hole, but when I pulled in after a test drive of about 5 miles, there was enough fluid on the shifter side of the tranny to drip onto the garage floor and leave about a 3-4" puddle.
Any ideas?
Thanks

[Bob W]

The hole in the top part of the tranny case that I am talking about, actually comes out horizontal. ( in the same orientation as the shifter shaft.  It is on the top left side of the case, on the "body" part of the case, not on the "bell housing."  Is there a website that shows 350TH diagrams and/or parts lists?

[Bob W]

a picture is worth a thousand words.....just remembered I had this.  The hole is the thing you see in the picture above the shifter shaft.  Can't really tell by this picture if there is something more than just the hole and the boss.

[Bob W]

so I guess I'm having trouble attaching the picture.  gotta go get the dogs rabies shots, so I'll deal with this later.