The most likely cause is an issue with the valve body.

The only way to check the transmission fluid level and condition is to raise the vehicle on a hoist. There is a fill plug that needs to be removed when the transmission is between 30 and 50 degrees celcius.

I recommend you take it to a Dealership, at least for diagnosis.

It is possible if you had a bad enough leak.

The only fluid that can be used is Shell LA 2634, BMW Part No. 83 22 9 407 765.

Unfortunately, the only place I know to get it is the dealership.

To check the oil level, raise the car on a level hoist, bring trans fluid temp between 30 and 50 degrees celcius and remove the fill plug (located in the rear/center of the oil pan) which is a 17MM allen screw. With the trans temp between 30 and 50 degrees celcius, the fluid should slightly trickle out of the fill hole. If no fluid comes out, fluid needs to be added.

If the valvebody needs to be replaced, the oil pan must be removed and all of the larger torx screws in the valve body must be removed to remove the valve body. The valve body replacement is pretty straight foward but if you are going to replace it, I can scan the com plete instructions for you.

I'll send it for you when I get home today, I don't have a scanner at work.