Have mine done preventive at 50,000 km(31,068 miles) by my BMW dealer !
But only with the best DCT fluid and recommended by BMW .
The OP part nr of the DCT fluid is ok for the US,in Europe we have other part nr but the fluid is the same ,brand name is
Pentosin FFL-4 ,this DCT fluid is also used by Porsche and is actualy the best fluid for our DCT
But one thing i know is.....Pentosin is $$$
When i get another 30 K miles i do the same thing...DCT fluid change !
Links to Pentosin...........
http://www.oilprofi.by/netcat_files/...L-4_V6_GB_.pdf
http://www.crpindustries.com/pentosi...osin_FFL-4.pdf
http://www.fcpeuro.com/products/bmw-gear-oil-ffl4