As you're standing at the front of the car looking at the engine, mine (1994 C280) is on the left side of the engine, almost at the firewall. It's a black squarish plastic knob. Note that there's a locking collar-- put your palm on the top of the black knob and where your fingers would touch there's a half-moon collar that rotates out of the way. With that collar "up" the dipstick will pull out of the tube. Remember to keep the engine running when you check... I've heard it best if someone keeps it in DRIVE with the engine running as you check it (unless you're in California, in which case that causes cancer).