The number one reason for an Opti to go like that is as you stated, failure to properly warm them up. I always wait till mine is 120° even during the day when I have been on a bank for quite a while.
Bruce Tangora at Tangora marine in Nixa has been doing motors for a very long time. I had him do one for me a few years ago and wouldn't hesitate to call him again.
Brian Hyter at Ulrich Marine in Branson West is a very good wrench also.