transmission leak, not front or rear seal but a small plug...what is this plug next to the drain plug

to anyone who might have a answer for this, I have a 91 v8 audi quattro all wheel dr sedan and I have a transmission leak, I have determined that it is not a front or rear seal. It doesn't leak from bell housing or rear shaft but right in-between, next to the drain plug "which is a inch an a half bolt" there is another but smaller plug the looks like the drain plug but is not, just in front of the drain plug, and this is where it leaks, does anyone know what this particular plug is for? is it a sensor? no wires or harnesses hook to it. Is it something to adjust the transmission in some way? does anyone know what this plug is for??? it must be fixed due to the trans fluid dripping on the exhaust and smoking very bad, any suggestions or answers would be greatly appreaciated