I realize there is a recent thread with similar discussion, but I need a clear suggestion for my particular situation. My 99 Lesabre has 207k on it and transmission fluid is almost black, foamy and smells burnt. My girlfriend'* mom owned the car for past 8 years, beat on it quite a bit and as far as I know never once had tranny serviced. Obviously it doesn't get up and go like new, but doesn't slip at all and shifts fine. In tech school my instructors warned me replacing fluid could mean the end, but if I let it continue I don't know how much luck I have left either. Do i drop the pan? Full flush? Im really torn on this...

what ever damage is done already sounds like. i dont know why people say dont do the proper maintenance, my only fear would be wasting money on a trans thats already done. if it hasent slipped though might be worth it

Typically in a situation like this, the clutch material is suspended in the fluid. Which is why its black like that. Once you drain all that oil out, you lose most of that clutch material. This is where the slipping begins because the old oil had that material in it.

I say leave it alone. The damage is already done and its now a matter of when it decides it won't work anymore. A rebuild IS in the future. No magic in a bottle will fix this either.

Mike is right, but there is a small chance you could change the fluid and not have any issues for a while, a while back I had my transmission start slipping, so since I had not changed the fluid in a while I decided to drop the pan, the fluid was black, and smelled a little burnt, still I went ahead and changed the filter, because reverse was not working well at all, so I had no choice.
As I was changing it I found out why it was slipping in reverse, and occasionally in drive, I had some pieces from the forth thrust clutch washer broke apart and clogging the filter, so I put the new filter in, and topped it off with new fluid, this was around 1,000 miles ago, and I have not had any issues yet, but I know it is just a matter of time.
I did use a rare earth magnet, and ran it through the old fluid to be sure there were no metal flakes or bits, if there had been I'd probably of put 50/50 old/new fluid back in.

Your best bet would be to save up for a rebuild, as the time will come sooner than you want it to.
I'd baby the car, and not drive it hard..