I'm not one to let something go. For example, when I bought my current '08 bass cat last year, I went over it carefully, but somehow missed a hydraulic steering issue. About a month later, turning left into our launch creek, the steering sort of skipped. Very much like what I felt when cable steering wore the teeth down at the helm. I knew instantly what it was, and added some fluid. But I knew that hydraulic fluid just doesn't evaporate magically. So I went on a careful quest and found the cylinder seals leaking barely. Replaced them and the fluid level has stayed static for a couple of months of fairly frequent use. Some might just fill and keep going. But when something changes I prefer to track it down as soon as possible, as it will generally keep biting at you until it reaches some sensitive part of your anatomy. :)
This slow turnover is not normal, and not endemic of these motors. So something is up. Whether the OP takes the time to track it down or waits for total failure, it WILL eventually be discovered.