Input from Mark Erskine – ‘Reviewing the above photos, in particular the ‘work in progress’ one, I see a note on the engine photo that the owner has used 5W 30 synthetic oil in the engine and gearbox.

Generally, older diesel engines have larger internal clearances than modern engines and (generally), a 5W 30 synthetic engine oil is used in a modern, close tolerance, high revving petrol engine. 

Older diesel engines have piston ring, cylinder liner and bearing materials that require a basic, heavier viscosity, mineral oil, such as a heavy duty, high detergent / dispersant / SAE30, SAE40, 15W 40 or 20W 50 grade.

I recommend the owner contacts either Castrol or Shell technical services for their lubricant recommendation for that particular engine and the gearbox.Tthere are a lot of old diesel and petrol engines in older boats and using the wrong oil can damage the engine.’