I was reading the cadillac forums and an individual by the name of bbobynski was posting the dangers of transmission flushes. He supposedly is a GM powertrain engineer for 32 years and he is against the transmission flush. The pitfalls he mentions are: The last vehicle that was hooked up to that flushing machine was probably on its last leg and was generating tons of debris. Most owners, when the transmission starts to act up, rush to get a "flush" in the hope that it will cure the problem. So...flush machines, by definition, see the worst of the worst. If the lines aren't cleaned, hooked up improperly, oil is re-used or recycled, etc.. then you are screwed as your transmission gets the dose of debris from the last transmission. He says that no matter how good the intentions of the shop, one simple mistake and your transmission gets the debris. He then mentions that Transmission Flushes are money makers for shops and dealerships because they are quick and easy and they can actually charge more money for it under the guise of it being better for the trans.
Harryface, has your bonneville with close to 300K miles had flushes or just fluid and filter changes? I know you have had a transmission rebuild but you seem to have good luck with the number of miles your parts last.