1995 Chevy Truck Is it worth repairing

The only one that can answer the question is it worth repairing, is you. I don't know what has been done to the truck or what the body is like. As far as water being in the diferental that could have happened if you went through a lot or deep water. With reference to the leak, check the hoses from the heater. They could have a pin hole in one or the clamps might need to be tightened or the hoses replaiced. The only other place woul;d be from the back of the intake manifold. Check the jhoses first to see if you can find a leak there.