IWC Cal. 401, similar to Cal. 89, Watchmaker needed.

Hello all, I have been waiting for a quote for two months from a watchmaker that did good work on my Rolex 1500 Date. It is a large shop. Anyway I am considering asking them to send it back to me. I have a Cal. 401 which is based on the venerable Cal. 89. It is running fifteen seconds slow and due to a lack of service history, I would like to service it.
I am in the US and am hoping for recommendations.
Thank you in advance.