Transmission Fluid debate
 

I don't get it. I've been attempting to simply drain and change the automatic transmission fluid in my 2007 Mazda3S. The dealer said I must only use Mazda's fluid, known as "ATF M-V" and none other. The local auto parts store said that is nonsense and that "ATF Mercon V" can be used instead. The Mercon V container even listed Mazdas as one of the vehicles it can be used in. So what gives? Are they interchangeable or not? Can they be mixed, since a simple drain only replaces parts of the total fluid in the system?

per the owners manual - ATF M-V so the dealer is correct... Though i'd bet that it stands for ATF Mercon V - same stuff.