As was explained in previous posts those "freeze/expansion" plugs are
nothing more than ports used to pour the iron into mold during the casting
process.....they are not really "freeze" plugs but fill plugs. They are
also useful in removing water from potential low spots by removing them when
winterizing.

Rather than guessing or taking incorrect advice why not take it to a marina
or dealer that services and repairs Volvo Penta engines?

Thank you very much for the information. If it does turn out to be
these plugs it will be of great relief.

Have a wonderful evening!