Are you familiar with Murrays.com? They are a great source for cat parts. See "Rudder Cam Kit" item #01-2050 (listed under catamaran / rudders, etc). I would drill out the old casting carefully to the exact size needed for the new sister screws, then replace. Do not let the drill spin free as this will give an unwanted angle to the new cam. I usually replace these on a need be basis which is whenever one begins to fail which is now rare. No more drilling but just unscrew the sister srews and replace with new cam. I do lube every time I sail with Harken McLube.
Jim
F18
H16
Sunfish