Fluid for powertrim unit

[Boatbudd]

This has a small leak. For some reason I put power steering fluid in years ago. Now I'm told it should be 10W40 engine oil. What should I do now??
Engine is 4 cyl Olds?? Serial # 85157913 Mercury stern drive #5199120 MCM140 I think 1979

 

[dubs283]

What should I do now??

find the leak, repair it

remove as much of the old fluid as possible and re-fill system with 10W-30 or 10W-40 motor oil