Transmission leak

I have a 1970 911E coupe which has taken to leaving a few drops of transmission oil on the floor. I jacked it up put it on stands and rolled underneath to find oil on the front engine/transmission support. It looked like it was coming from a fitting on the right side of the transmission and to the rear of the support - is this the speedometer cable, I can't find a picture of the transmission that shows it. Anyway, pushing this object showed it to be a little loose and there was no room to get a wrench on the nut at he base of it.

I guess my questions are - is this the speedo cable and if so how do you tighten whatever it is without lowering the transmission