Our 1980 Nauticat 33 shows signs of a previous owner’s efforts to shore up this same area using wedges and thick fiberglass structural material. Symptoms of a structural problem include: The sliding door between salon and foreword is very difficult to move and the cabin top where the main mast steps is located is depressed.
I understand that during this period of Nauticat construction, design changes, without proper structural changes, may have caused this compression problem.
Your description suggests that the “jack screw” was an attempt to fix this. Why it does not adjust is a puzzle.
Good luck! Look forward to hearing more.