Every MB has a drain plug on the oil pan, its a myth that they removed it in the later cars. The trani dipstick tube and oil dipstick tube can possibly be right next to each other against the firewall. if you remove the airbox you might see two tubes. One will have an all red cap that usually sits higher tyhan the other and you can just pull it off, the other will be black with a red insert stopping you from being able to pull it out. The all red cap is the oil dipstick tube, the black with red insert is the trani dipstick tube.