If your transmission croaks after a fluid change, it was ready to go out anyway. That's my opinion. If you have 100k on a tranny without any fluid changes, it's already on borrowed time.

If you don't have a converter drain plug, the BEST way to do a change is this - yes, it's a bit wasteful but it's the RIGHT way - drop the pan, clean it out, and change the filter. Top off the fluid and take it to a shop that has a flush machine and get a total replacement.

 

+1, I've been saying that for years.

Remember, all flush machines are not identical. Many run on a piston and it is mobilized by the transmission in the car itself, not a "backflush."

As new fluid goes in, the old fluid goes out.