I just had the exact same thing happen to me on my 03 Maristar 230. You need to find out which control box you have. I ended up buying it from the dealer as I didnt know. Yours looks very similar and maybe identical to mine. For under $200 I ended up getting the entire control box. If you dont want to replace the whole assembly, you can take the arm assembly from the new control box (it ships already separated from the control box) in the shipping box. Then put the new arm with your new knob, onto the existing control box on your boat. The hardware is included. The new unit makes it easy to see the set screw you need to remove to get the arm off the old control box. Good luck.