From an experienced marine engineer
and delivery captain
Rig a engine
(not pre-filter) fuel filter
to filter the oil
if you think you need to.
I've never had to do that in twenty years as marine engineer
. If there is enough metallic dust that on a black cloth you can see shiney particles you should think about full overhaul
Would recommend changing the oil if you know its old though...
Dark hydraulic fluid is normally hose degradation contaminants - in the long term plan to change the pipes and oil...
Hope this helps