Does any one know why Motorcraft VC7 "gold coolant" is recommended for '02-'05 Excursion and the '00-'01 Excursions get the green coolant VC5. What changed between the model years that would require a change in coolant? Why isn't VC7 backwards engineered/approved for '00-'01 Excursions like Mercon V was for their transmissions?