I just installed the CH2100P today and had to use an electric cut off tool to get the chrome ring off. It had bonded with the shaft over the past 33 years. Once that was off I had to cut through the "nut" that sandwiches the control in place.

The instructions came with a template that was used to make the new, larger mounting hole.

I got the CH2100P from Go2 Marine ( no affiliation ) for $170.

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