I feel your frustration... All I can suggest is buy yourself a new stock standard Volvo Penta Aluminum prop and your problems
will go away. Sounds like your boat dealer is spinning you a line and now getting tangled up in his own BS...

or he is just plain incompetent...
Buying a genuine new Volvo prop (make sure it is real Volvo prop and not any other brand) won't cost you a heap of money, but will definately fix your problem, give you more time on the water, and is a hell of a lot easier than towing your boat to the dealer each time. This will establish a known good working factory base line for you. Then you can try other props, but always have a known good combination to fall back on.
Sounds to me like your dealer is simply guessing, or trying out each of his repaired props in the store until he finds one that will work for you. I have never been a big fan of repairing props - they never seem to get it half way as good as a new one and the cost difference between a repaired prop and a new one is not huge. Your story simply reinforces this.