[RMS]

To remove the stuck zinc, cooler removal is probably necessary. I would not rush into that however. What I would do (and have in the past) is insert the new pencil zinc and take the boat for a ride. If the engine is not running excessively hot, leave it be.

I notice your home port is fresh water. In salt water (my home port) I would replace the pencil zincs twice a year to prevent the anodes from breaking off. Going forward, check the anodes every few months and replace as you wish.

Bob