Grey smoke is generally not possible on a diesel
engine. You need to decide if it is bluish or blackish.
Bluish is burning oil.
Blackish is overload from restriction or from prop wrap or fouling of the hull
I would monitor
fluid levels and hope for the best.
Actually if it was my engine I would stick my hand in front of the exhaust
and wait till my hand got dirty and then I would smell it and feel it.
I also might look in the freshwater system for signs of oiliness and or bubbles at temperature.
I would also drain some oil and look for milkiness or water.
But if I didn't find anything and the smoke was pretty light or intermittent I would probably motor
on with a careful watch and hope for the best.