Good evening to everyone, My Mazda6 (in signature) uses a 75w90 gear oil in the manual transmission. Surprisingly, nowhere in the owner's manual does it say anything about servicing the manual transmission. However, the lubricant spec'd for the MTX is API Service GL-4 or GL-5 75w90 My previous car (Saturn SL) with a 5spd manual transmission used ATF fluid rather than a gear oil and I was advised from the Saturn experts that the ATF in the transmission didn't require any service. From what I have gathered changing my engine oil the transmission has an easily accessible drain plug and a fill plug. The manual says the transmission uses 3 quarts. A few questions: 1. If there is no recommended service interval how often should I change the gear oil? I assume like any typical oil it will break down and eventually sludge if not properly maintained....although the lack of "heat" shouldn't stress it too much. 2. How does one actually fill the transmission? Do you use a plastic flexible tube with a funnel and simply pour the oil in? Must this done be performed on a lift so the car is flat rather than on jack stands? 3. Would I be wise to use Mazda MTX gear oil or could I use any 75w90 gear oil that meets GL-4 or GL-5? Is GL-5 "better" than GL-4. Some claim the GL-5 is harsh on syncros? Thanks in advance.