I may misunderstand what your asking or your
OMC is different than my Evinrude.
I believe rubber seals are what your missing.
Anyway this is what I have done. Found a
rubber hose that fits and cut it slightly longer
so it will compress when the to sections are
joined together. I also had a soldered joint
that failed so you might want to check all
of yours.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.