Keith, you are being very brave asking for help on here. You are already a very experienced trainer and many of your posts show that you have excellent dog sense. It is easy for beginning trainers to ask for advice, they need knowledge and are grateful for any help they get. It takes real courage to ask for advice when you face a problem that your years of experience tell you you should have solved. Sometimes even the best of us lose sight of where we are with a problem because we are so deep in it...this is why brilliant writers need their editors, or great recording artists need a producer to bring out the best in their new song. A second pair of eyes often gives a perspective that unlocks a problem or spots an error that the first person misses.
It feels to me like you might be digging a hole for yourself with some of your reactions, perhaps you feel a loss of pride because you are getting advice that you didn't come upon yourself, that is not an uncommon response....but isn't that why you took the risk of asking for suggestions? You are getting the benefit of a second set of eyes on your problem with this dog, this isn't criticism of you as a trainer, it's the help you asked for. Thank you for bringing this problem to the forum, you and everyone viewing are getting a great opportunity to learn.