actually that's a good question...lol - and on some cars it is and some cars it isn't. On some cars it's called power assist where the rack is sealed (w/it's own grease) on others PS fluid/atf fluid runs from the res, to the pump to the rack. Your best bet is to trace the hoses. In any case a leak is not good. A little seapage seems to be common on BMWs at the res. Another good point to note some use ATF and others use a special fluid by BMW check on the lid of your res or on the little dipstick withing the cap/res.