I have for sale an Alpina deep finned aluminum oil pan for the 6HP26 trans. This will not only add capacity, keep the trans cooler, it is also not prone to leakage like the plastic pan. It also uses a separate filter, unlike the stock plastic pan which has an integral filter. This pan is $1500 new,
PRICE DROP NOW $700 with a new gasket, and filter. The only thing you will need to modify is Dremel out your plastic trans splash shield to expose the aluminum fins.
Pics added Edit this will fit other cars with this pan, E60 545/550, E63/64 and X5's E53 and E70 with N62 engines.
http://realoem.com/bmw/showparts.do?...84&hg=24&fg=15