I could be wrong, but I'm pretty sure there is a non-documented dipstick on the 35d (I don't actually own one yet). It's mentioned in the N57 technical manual, but nowhere in the owner's manual and not in plain sight.
See item 10 on RealOEM.com parts:
http://www.realoem.com/bmw/showparts...88&hg=11&fg=10