My 18 (#555) is an older one, and I just gave up on the rudder adjustments altogether.

I drilled a ¼-inch hole through the highest point of both castings and inserted various items to act as a "shear pin".

Here's some that have worked fine for weeks at a time: short sections of nylon knitting needles, chop sticks, wood dowels, and just plain old wood twigs from the woods.

Just like shear pins for outboards, I carry spares.