Many thanks for your prompt reply, which is most helpful. As a temporary repair and to eliminate further wear as well as taking up the slack between the gudgeon and pintle I'm thinking of slipping a piece of tight fitting nylon tubing over the lower rudder pintle. The existing pintle is pretty worn but I think it still has plenty of strength.
The yard where I keep the boat told me that the dagger plate was jammed solid but after removing the pivot bolt which was well worn, they cleaned up the plate and primed it and I'm hopeful it will move easier when reassembled.
As an aside, my road trailer wheels were seized but on taking off one of the wheel hubs the brake assembly was fine and the problem was the brake cables had rusted and jammed in the on position. These having been cut the calipers sprang back and now the wheels turn freely. Obviously the cables will need to be replaced before I can use it on the road but I'll be able to get the boat to the water. The piggyback trailer had to have new wheels and tyres as one of the tyres exploded when the boat was being brought up last September.