I have a system that is pressurized but has no method to put the pressure in automatically, which I thought it did. I never even thought about it other than to look at the fluid level in a clear window in the resevoir can.
This Spring, after 5 years of owning the boat, I lost steering - I mean it was complete, no steering at all! Traced the hydraulic lines to that can on the stern with an airvalve on it and a little label that says to keep the pressure above 30#, I think. No pump of any kind in he system.
So I got a bicycle pump and aired it up and, voila, steering is good again. I'll have to check that from time to time. Could you have a system like mine?