Definitely a leak. Could be the pistons need rebuilding or it could be leaking at any of the connection points. The reservoir or even the pump itself. Trim the motor up and down and look for the leak. It is a fairly simple system so you should see the fluid coming out somewhere. If you don't you can put clean rags or paper towels at all the connections to help you find the leak.
Had to rebuild my pistons after about 10 years on my old boat. -- Good luck.
