Contemplating an ATF drain and fill on our 2001 Ford Expedition. Last drain and fill was done about 3 years/20k miles ago. Vehicle now has approximately 169k miles. No real problems with the way the vehicle is driving, just considering it for preventative maintenance. Dipstick is labeled "Mercon". My question is use of fluid that is not strictly Motorcraft Mercon fluid. Based on what I've seen on-line, looks like it's difficult to find anything that is a "true" Mercon fluid short of a multi-purpose Dex/Merc type fluid such as Mobil's ATF D/M or Castrol's Transmax Dex/Merc. What would you suggest?