Vehicle is <12 months old Merc S350 diesel. Suffering constant loss of coolant. Clear signs of 'pink' crystals in area of water filler and associated pipe work. It is as if the coolant is being forced out under pressure. Booked in to local Mercedes garage however have had bad experiences with Mercedes dealership which sold me car (not local). Any comments on possible causes (and what I should be asking Mercedes to check) gratefully received.
Check if you have excess coolant in the reservoir, the coolant is oozing out during the expansion, at this point with the data you gave I am not sure if the car is over heating or not.
Check the max and min levels on the reservoir and adjust the level of coolant accordingly. when the coolant from the radiator expands upon heating the excess flows into the reservoir and if the reservoir already had excess it would try to ooze out of the reservoir.
As it is almost a new car I definitely don't think its about the head gasket. Do check to make sure the cap on the reservoir is tight, there are no cracks in the reservoir, the level of the reservoir fluid, and check if the car is over heating.
Clean of all the residue off the reservoir tank, adjust the level of coolant and take it for a ride.