[kawishiwi]

OP got "screwed" by the marina/mechanic whether by laziness, incompetence, or even bad intention.
Being made "whole" physically should have included a full refund of expenditures minus the cost of the initial inspection that should have uncovered the real issue.
Being made "whole" should also have included a forthright acknowledgement that they screwed up.
OP got neither. One wonders at the ethics & conscience, or lack thereof, of the marina/mechanic.
BUT...not living up to your own agreements is just getting down in the mud with them. This is a question of the OPs ethics & conscience. I would encourage OP to take the boat just for the part removal. Not for the benefit of the marina but for their personal benefit of a clear conscience and a forthright statement of their ethics.
IOW, you will sleep better if you follow through.