The oil could be leaking from your transmission. BMW uses a light brown oil in their trans, however it will get a little darker over time as the trans wears.
The 2 common leaking points on these trans are the mechatronics sleeve and the front oil pump seal. The mechatronics sleeve is a more common leak. BMW has a service bulletin out for this problem.
SIB 24 08 06 Mechatronics sealing sleeve leaking. Trans fluid leaking from area of trans oil pan. (Should look like it is coming from the rear of the transmission.) Most shops would just replace the trans oil pan gasket which will not fix the problem.
(In the picture below it shows the trans electrical connector. The sealing sleeve is actualy the part that the connector screws into.)
If it is the front pump seal then the whole transmission will need to be removed. This leak will look like it is coming from in between the engine and transmission.
(In the picture below it shows the torque converter being removed to access the front pump seal.)
Cost all depends on where your located and where you go. Here is a rough estimate: The mechatronics seal is going to be 3 - 5 hours labor plus parts. ( probably around $700 or €444)
The front pump seal is going to be 9 - 12 hours labor plus parts. (probably around $1300 or €825)
Let me know if you need anymore help.
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