That's what I am afraid of too... someone told it if you don't change the trans fluid, you might drive it the way it is for years and not notice anything bad happen, but you might change the fluid and the next thing you know it doesn't go in gear when you start it up.

Also curious... what mileage did it need the rebuild at?

Mine did it with a factory filter (trans was replaced at 56k), and still does it with an OEM rebrand filter. I'd say it's nothing to worry about.

Here is where I think most people kill their transmission. After they drain and refill the tranny. They start the vehicle let it run and go through the gears........NO! Refill the tranny until it starts to back up out the side hole. Put the plug in, start the motor for 3 seconds or so and shut back off. Basically on and off. Open the side hole and the pan will be empty again. Fill back up until it starts to back up out the hole again (put plug in).....start for 3 seconds and re-check. If their seems to be a fair amount of fluid still in the pan, top it up, now it's time to put it through the gears one step at a time (not to slow) shut engine off and check again. If the fluid is at the hole, (then) run the engine and top it off. Just a very short period with the pan empty (or even too low,) if the pump draws air, this will damage it. This is where the damage happens when changing fluid. It's not magic.