I want to change the coolant in my 1987 560SL. I know how to drain the radiator, but I understand the block needs to be drained as well. The service CD indicates there are two drain plugs on the block--one on each side of the engine, near the motor mounts. I'm not sure I've properly identified them. I see two possible choices--a 17mm bolt that threads into the side of the block, or a 6mm hex socket that screws into the block. Neither looks to be very accessible. Anyone know for sure where the plugs are located? Appreciate any help....John Downey