First post here. Thanks for looking!

I'm looking at a 1999 ML430 that has a trans problem. I haven't actually seen it yet, but the problem described to me is that it's slipping (yeah, I know - not very specific). I didn't get any better description than that. It has 115k miles on it. My questions are:

1 - What are the chances that it's the fluid in the ECU thing or something else vs. just worn soft parts and the trans needing a complete rebuild? Are there any tests or things to look at when inspecting it to give me an indication?
2 - If it is just worn out, how much should I expect to pay for a reman/rebuild, and where is a good source for one?

Other than the trans, the engine runs good and it's clean. Of course, if it wasn't a very low price, I wouldn't be looking at it. T