On the 1999 C-280 the book does say 8.5 quartz and that may be true with a brand new dry engine,but if I put in 8 qts. I am over the max on my dip stick, with 7.5 qts I am midway between min. and max. on the dip stick.
On the 1999 SL500 the above applies and I put in 8 qts and got a dash board warning that I was over max and had to pump out a quart.