I've had that same experience with DA. Usually after I have had some service work done on an engine there, when I call to see exactly what was done (usually an improvement at no cost to me) they usually deny knowledge of things that are clearly visible on the engine when it came back. For example, recent carb changes that greatly improved my DA-50 midrange ... yet they said they did nothing to the carb and physical things on the carb were different. Its like the guy who answers the phone doesn't really know what the guys in the back shop are doing. Now this is not meant to blast DA in any way, my (2) DA engines perform very well and so far, I have never had to pay a dime for normal (not crash damage) service. But phone conversations with DA have usually left me wondering why I bothered to call in the first place.