Low Maintenance does NOT mean No Maintenance

Do a yearly inspection.

Look at the seals on the cylinder.
Especially on an open boat, where it's exposed to salt, sand, fishing line, and other potential hazards. The shaft should never be wet with oil. If it is, wipe it dry with a rag and check it again as you turn through a steering cycle.

If a wet shaft comes out of the cylinder, the seals are leaking and need to be replaced. Check for pitting on the shaft, a sign of corrosion that will ultimately cause hydraulic fluid to leak out of the cylinder.

Look at the hydraulic fluid. 
Remove the vented cap on the hydraulic reservoir at the helm and take a sample of the hydraulic oil. Does it look black?  Is it milky?  Does it smell? Hydraulic steering fluid is clear, mostly odorless, and light-colored. It's specially formulated with viscosity stabilizers, anti-wear and anti-foaming agents, and corrosion inhibitors.

If the hydraulic steering oil sample contains water, dirt, or is otherwise contaminated, the entire system should be flushed and the hydraulic oil replaced. Abrasive dirt is the biggest killer of hydraulic systems. It often comes from debris during the initial installation of the steering system. Dirt or dust can enter the system when hoses are cut and fittings installed. It's best to flush out a steering system before the final hydraulic oil goes in, something to consider when making a repair. Your hydraulic system should be flushed out and oil replaced every five years, including thoroughly bleeding the system to remove air bubbles.

Spend a moment at the helm.
Is there any oil visible around the seals behind the wheel? Does the wheel feel spongy when turned? It may have air in the system, which needs to be bled out. If the system was previously purged and all air removed from the lines, this may be a sign that there's a leak somewhere. A spongy wheel may also indicate the cylinder or steering pump is leaking internally, which you may not readily see. If you once enjoyed three-and-a-half turns lock to lock, and now it's five turns, you have a leak. Oil doesn't evaporate, nor is it consumed by use. So if you have to add oil to the reservoir, you have a leak.

Check the hoses and connections.
Wipe the hoses between the helm and the ram with a clean rag. Is there any wetness at the connections? The nylon plastic hoses that snake their way aft to the steering ram can get brittle and crack over time even though they aren't as exposed to the elements. The flexible rubber hoses are most exposed, but also easy to inspect.