Behr radiators for various Mercedes models, like the W201 and W124, have plastic necks. However, I have found that there's a connection between the plastic neck failures and failed motor mounts that allow engine vibration to be telegraphed through the radiator hoses, not the coolant.

I wonder if the change to blue coolant also prompted the demise of ATE's Blue Racing Brake Fluid, due to the risk of consumer's mixing it up with windshield cleaning fluid, coolant, grape juice, huckleberry syrup . . .