This. Flushing a high mileage tranny can cause all the crud to dislodge from places they weren't currently harming anything and cause some real damage depending on where they land next.

And you can only DIY flush using the tranny cooler lines which I think is safer than having a shop hook up the machine. Using the trannys own pump seems safer to me that a third party pump. Just IMO.

 

I was a quart low and the tranny started slipping so i accidently put a quart of merc III in by mistake..it made it about a mile then i lost all gears.. Towed it home and dropped the pan...now what? Change filter and fluid or is it a total loss?