Trans Slipping

Anyone ever had this ?
My Automatic Transmission is starting to slip, usually when first starting and again as it goes into 3rd and while at normal highway speed.
The car is a 96 SL-1 with 224k+ miles on it.
Anyone whow what price range it would take to have one of these puppies fixed or replace ?
Or if it's even possible as a do-it yourself?

I dont know how much it would be to repair one of our transmissions but a used one would probably cost in the neighborhood of 500 or so. To change it you have to take out the motor and trans. together though.

I dont know how much it would be to repair one of our transmissions but a used one would probably cost in the neighborhood of 500 or so. To change it you have to take out the motor and trans. together though.

From what it looks like is the seals are leaking, several if not all, but it's been too cold and wet to o anything as yet. Added some slick50 trans fluid and brought the levels back up with new juice. Haven't road tested yet though to see if that was just it or if it's still slipping.
Only other car I've seen in the same class for dependability is a Festiva.
At 225k it's getting up there, but don't want to do anything too costly repair but would rather not replace the vehicle.
Any alternatives are an option.