I recently bought from an auction a 2001 bmw x5 e53 4.4L.

About 120k miles on it.

I changed the battery to a new one, the car starts but a few days later the battery is dead. What could be the cause?

Also the tranny seems to be messed up, does not take first gears, but it will take reverse. I have read this is a common problem with this cars.

The mechanic change the oil and filter from the engine and so it did with the tranny. THe car will only take gears from the M not from D. THe computer scan came up with only an error of speed sensor or something.

Where do I start from this point? Try to get it fix or seek for a mechanic that knows more about bmw trannies?

I have own vws and audis but its the first one I buy with tranny issues.