"You've discovered yet another defunct Claptrap. Doubtless, he wandered in here and was destroyed by the inhabitants of the cave. Perhaps there is a Repair Kit nearby?"
The Claptrap can be found at a small clearing area in the Lost Cave where there are some bandits. The first image shows the location of the Claptrap on the map (where we are standing, not the waypoint). The second image shows the in-game area.
The required Repair Kit can be found a little further into the Lost Cave. Just before crossing the bridge, the Repair Kit can be found in the end of a pipe. The third image shows the map location, while the fourth image shows the repair kit.
This Claptrap, upon being repaired, wheels around the area it is found in. It will offer a reward of a Backpack SDU on the first playthrough. On the second playthrough the Claptrap will offer either a Backpack SDU or a Grenade Mod. If the character's backpack is full, the chances of receiving the Backpack SDU will be higher.
"Thank you, kind traveler! I can now return to my assigned duties. By the way, I found this. You look like you could use one of these!"
Claptrap Repair Kit: Contains everything you need to repair a Claptrap robot.