jms,
that is fairly typical in the industry, as Hunter more than likely does not provide the 5 year extension nor possibly the gear in question. You would be best to go back to the folks that sold the extension. Sadly if you are not next door or at their dock, you will pay for a service call.
As a boat mechanic, I have to side with those who will not do the work and then hope someone pays them back...A small shop can not afford to do all the admin and gamesmanship that the extended warranty folks will make them jump through.
Since much of that gear is "added on" by someone other than the builder, builders are hesitant to get in to the finger pointing game either.
Your only real choice is to have it repaired to your satisfaction and at your expense, keeping and asking for copies of all bills/estimates etc. - and then forwarding (fighting with) the folks involved yourself. There should be no problem asking your mechanic for copies to submit, if he hesitates or will not - find another mechanic.
Hopefully your 5 year extended warranty is still useful, as several have posted here that the company that provided/underwrote them has gone bankrupt...so there is no longer an extended warranty at all...
YMMV, and best of luck