My apologies, I thought several others had posted with the same problem. I must be thinking of a different forum.
Is this a Volvo? If so (may be the same for Merc but I'm not sure), assuming your "rams" (hydraulic actuators) nor hose fittings are visibly leaking, the culprit is most likely to be the check valve inside the pump assembly. This diagram is probably not exactly a match for your unit but should give you an idea of what we're talking about (see index #42):
That's from http://www.marinepartseurope.com/en/vol ... 10430.aspx.
Some pumps have two check valves, high and low pressure. In this case I assume it would be the high pressure one leaking. Most folks will replace the whole pump to fix it ($$$$), but in reality I believe you can repair it if you can track down the parts. I don't know if it would be the ball, spring, seat, or all 3 that you'd need. I haven't had this problem (yet), so I'm afraid that's about as far as I can take it.
You might consider adding your boat, engine, and drive details to your signature, it can really help people get a head start on what the problem might be, when you have one.
