Looking to buy a X5 but needs some work

[smokeyyank]

Howdy,

As stated looking to buy an X5. Came across this https://denver.craigslist.org/cto/5944250040.html and caught me eye. I haven't had a chance to look at the car yet (damn snow), but wanted to get some advice before going to look at it. In speaking with the owner, BMW says tranny needs to be replaced because they don't service them. Indy shop looked at it and just said it needs to be serviced not replaced. Owner says no codes come up and car will drive but in higher gears will slip. I am extremely handy so not worried about having to tear into the thing and this would be a second car. My thoughts off the bat are low fluid/fluid issue, valve body or TC. Any other ideas or things I should look for? Thanks