Thanks for all the comments and ideas. At this point - I took the bike to a different dealer so get an another perspective.
They found that the post was nearly .03 - 05mm smaller in OD than the stated size. Something like 26.55 to 26.57 on a 26.6 post - we both admitted we didn't know if that was an acceptable fit.
The mechanic tightened the bolt using a a shop quality torque wrench - and I have put another several hours of use on the bike without the post slipping.
Here's the deal - I know I had already tightened that bolt to "very large" amount of resistance using a 4 inch allen wrench. That was in August of 23 - I've never heard of a binder bolt just "loosening" up due to time or miles.
I should have had that mechanic measure a couple of other posts just to see if the micrometer measurements vary much. In any case, the post height is marked - if it slips again within this season - I have things too try.
As I said - I appreciated all the ideas - I'll use this thread as a reference if I have trouble in the future - you're never too old to learn something new.
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