The oil appears to be coming from the lowest point of the housing as
it emerges from the stern. Based on the size and depth of the slick,
something is weeping slightly. To give a basis for comparison, a
finger dipped in engine oil and immersed in the water produces a
slick of equal or greater magnitude.
I am not obviously losing oil from either the engine or the stern
drive. Neither oil shows any sign of cloudiness.
I am guessing the source is one of the seals on either side
of the universal, either the engine side or the drive side.
Other possible sources a hydraulic tilt or hydraulic trim tabs,
but the location rules out the tabs.
(1) Where do you think the oil is coming from?
(2) Can the source be checked with the boat in the water?
(3) Is the source so slight that the shop will have trouble
finding it even with the boat in dry dock?
(4) How often should seals be changed as part of preventative
maintenance?
Many thanks for your kind assistance?
Frank