When push comes to shoove as is the case with my very old P16 castings there is an old trick with 1 inch diameter plastic hose.

Cut a few pieces of this hoose about 3 inches long and jam them between the casting and the sterns. The friction between teh alu casting and hose is less than between the gelcoat and hose. Therefor the hose will stay on it place and tighten up de rudderassembly while not really introducing much extra friction in steerage. An added advantage was that the rudders are less like to turn when you lay you tiller bar on the deck. This was helpful when raising and lowering the spi singlehanded or when tightening my downhaul which I can't set from the trapeze.

Wouter