Originally Posted by Richard B
Technically you are supposed (recommended) to replace the hydraulic fluid annually as it is hygroscopic - that is, it absorbs moisture. This degrades the fluid as well as potentially damaging internal components and seals.
This is the same advice as with changing brake fluid on car brakes every two years that most of us ignore.
I have not changed the fluid on my hydraulic steering in five years - but sods law will probably prove me wrong later this season ?!!