I just went through this on a couple different vehicles and talked to a lot of people, some mechanics, some just the armchair old timers. It seems most of the crap that is in your transmission accumulates on that big nasty magnet on the drain plug...which makes sense. As far as the fluid breaking down, everyone seems to agree it can go a very long way. After filtering through (pun) the advice I received, it seemed like the best way to go was to replace the fluid and trans filter and add a bypass filter which would filter the fluid down to a finer level. For extra safety you can add one of those filter mags through summit or whoever you know carries them. Personally, im considering just getting some cow magnets, ziptie them together and drop them in plasti dip and strapping them to the filter. The full flush seems kind of like a dealer ploy after all the info i got. They'll even change your blinker fluid and re torque your whirly gig for only 399 extra.