Flushing should only be done when the transmission has under 30K miles. After that initial flush, every 30K following it, and you'll be fine. It actually works very well.

However, if your transmission has higher miles on original fluid (above 50-60K) what happens, is all those deposits that have begun to form, due to the fluid breaking down, are swirled around inside the transmission, usually getting stuck in and around the valve body. What this does, is, starve the transmission, resulting in it's demise.


My Town Car has 130K on it, flushes every 30K since new, transmission still works like new.