John,
On a left hand drive car, the windscreen washer pump is located at the top of the left rear-most corner of the engine compartment. It is approximately 9 cm long, mounted horizontally. The washer fluid bottle is located between the break booster and a small metal "shelf" mounted on the left inner fender panel, just forward of the pump. From there you can trace the fluid lines. I just replaced mine and they are available from Mercedes.
Regards,
Stan