In old vehicles, if the automatic transmission sits for awhile without use (e.g., 3+ months), the seals get hard and leak. This exact leak has happened twice on my restomod with a Ford C4 automatic transmission (sat due to mods being installed). Researched and found ATP Automotive AT-205, used it the first time and it worked like a charm So I used it again the second time (about three years later). It supposedly freshens up seals (flexibility). My leak was around the shift controlling shaft out the side.
As to the idiot light, I assume it’s because the fluid level is low, but you should get it read. A local independent shop should read it for a lot less. Some auto parts shops read codes but may not be able to read BMW codes. You could buy or download a BMW code reader. Good luck!

 

to start with, getting your hands on a handheld BMW specific scanner will pay for itself in less that one use. then you can get the code(s) the car has stored and post them on here. without the codes, we're all left just whizzing in the wind.
and welcome to the fest!!!

 

^this^ You won't need to invest a lot to get a decent scanner capable of reading BMW specific codes and will also be capable of handling 90%+ of DIY repair needs. And yeah, they usually pay for themselves the first time you NEED to use it.

 

plus a BMW specific scanner will allow you to read ALL the modules of your BMW car, OBDII readers will only allow you to access the DME (engine) and the EGS in some cases (transmission). if you plan to stay in the BMW ownership world, you will need the scanner, and you only have to pay for it once.

 

The most common cause of leaks with the ZF 6HP transmission is the mechatronics sleeve. Most of them failed early and under warranty but for those of us with ultra low mile cars, the leak comes after the warranty has expired. The fix is not that involved except you have to drop the (non-reusable) transmission pan to get to it. Figure on just under $1,000 from an independent and about $1,500 at the dealer. The parts are sold online as a kit (pan, bolts, fluid, sleeve) if you think you can fix it yourself.

Oh yeah, like the others said, get a BMW specific scanner.