There have been quite a few recomendations and a number of self-recomendations for brokers to replace AUA, if necessary.
1) DO NOT call all these brokers and ask them to quote. They ALL represent all the available insurers and they all can get you more or less the same terms. Involving multiple brokers won't get you a better deal. It will only cause you to have 3 or 4 brokers calling you and telling you that they have a great deal for you - each with incomplete market info. It will drive you nuts, nothing else.
2) Don't feel a need to jump ship with AUA immediatly. Your insurance contract is with Chartis - not AUA. Your coverage is not in jeporday and your policy won't be cancelled. If Chartis cancelled AUA's broker appointment, then, eventually, AUA won't be able to request service issues (policy changes, requests for certificates, pilot changes, etc) and they won't be able to renew. None of this is an emergency, unless your policy renews tomorrow.
3) Don't know what AUA's problems might be. But - insurers usually only cancel appointments because of premium payment issues or failure to maintaing Errors and Omissions coverage, or something like that. (Remember - you pay your premium to the broker and the broker has to pay the insurer.) The broker also has to maintain those funds in trust - if you cancel your policy, he has to give the unused premiums back.
4) If you switch brokers mid-term, the new broker will most likely not be able to return commissions on return premium issues. Make sure you know how you'd be getting the commission portion of return premiums back on mid-term changes. Probably worth a call to Chartis at the number provided on the letter they sent. Ask for Greg Sterling. He's the manager of the Light Aircraft Division (LAD).
Hope thus helps. Good luck.
Jeff