Thanks for the replies.
@Mees,
The seawater in the engine blocks occurred with new, flat faced seals
which I suspect to "aquaplane" and let water through.
These were used by the mechanical shop. I will not use those again and
I'm back to the "V-shaped" seals.

@Steve
I normally run the engines (I have a twin engine motorsailer and BOTH
identical engines show the same problem...) below 2000 rpm.
With the last overhaul, every bearing was replaced even when the
bearing looked and felt OK.

@Bruce
I think your solution is the way I want to go.
Which brand centrifugal pump did you install?
Any pitfalls or more hints come to mind?

TIA, Len.