Could be lots of things....and not knowing the history doesn't help.....
I'd start with a complete inspection....leaks, loose fittings, damaged tubes, etc.....if there is nothing found, verify the fluid level and condition....topping it off may be sufficient but suggests a leak that is small but been around a while....may need a complete drain, flush, and refill.
I've never seen a helm unit that needed major work....they appear rather robust....the cylinders stand up pretty well as long as they are properly sized and well maintained....