speed-o-meter issues

[kmfb]

so I recently bought my 79 and have been fixing all the little issues. My cluster I believe is a later year cluster, at least I know my bezel is for sure. It has a tach on the left and speedometer on the right. Neither work! I had my truck up on stands to change the rear end oil and thought id crawl around and look at the tail cone to see if the cable was hooked up. The cable is a 2 part cable that runs down into this little gear box lookin thing. Everything is in place but the box is loose to the transmission. When I wiggle it, it leaks tranny fluid alittle. Does anyone recognize this box? p.s. sorry about the funny angle, i was on my back in an awkward position! Thanks in advance!