According to the 2001 manual, p. 187, the capacity is 6.9 U.S. quarts with a filter change. Maybe last time they didn't drain it properly? Anyway, I always to fill it to one quart less than capacity, then check it with the dipstick before putting in the last quart. That way, if I didn't get it all out, I can judge how much to put in out of the last oil can. It's a bit tricky with the M5 however, since the check procedure requires engine start up and run, then a check after 1 min. after shutdown. Am I hurting the engine starting it shy a quart? Maybe, but probably not.
