Speedometer Working Sporadically on 92 4Runner

I've got a 92 4runner, v6, auto. The speedometer has begun to work only sporadically. In other words, sometimes it works, other times it sits at zero while I'm driving. As far as I can tell, there are no other problems that trigger it.

I know there are a couple of different types of speed sensors. My question is which is most likely the problem and is it something I'll be able to fix myself. Thanks in advance.