I am fixing up this pressure washer that was given to me. It has a Yanmar diesel single cylinder engine mated to a Cat Pump model 510. I have got the engine running fine. But I don't know a whole lot about pumps. When I run water through it, it leaks out of the bottom....where the plungers are...by the oil resevoir. What would cause this? Hope I explained it good enough. If not, let me know and I will post some pics. Thanks for the help.