Transmission fluid leak?

[demok83]

Hey guys, I noticed today some fluid dripping off of my transmission. My truck is an 83 silverado with a th350. It appeared to be leaking out of my speedometer cable. I tightened it and it has appeared to stop. It is also dripping off my driveshaft, and it appears to be coming out of it. Is that possible? Please forgive my lack of knowledge, I've just started working on trucks. It is a big learning curve, but I absolutely love it! What could be causing the leak? Also, I took a picture of something (last pic) that I didn't know what it was. Any help? Thanks!