Hit Wal-Mart, O'Reilly Auto, Autozone, etc. and get the stuff spec'd for it - ATF+4. You'll find it for $5-7 a quart depending on where you get it (O'Reilly has gallon jugs for $26-27).
As I understand it, the "ATF+4" brand or name or type or whatever it is just happens to also be trademarked such that you have to get approval (and pay a licensing fee I'm sure) to use it on your product. And to get approval, you would have to demonstrate that your product meets all the same specs that the AFT+4 fluid is supposed to meet. As such, not just anyone can slap "ATF+4 Transmission Fluid" on any red oil they make and try to sell it to you for your AFT+4 application. For it to be labeled ATF+4, it has to meet all the requirements and work in all the spec'd applications for which ATF+4 was originally designed and intended by Chrysler or whoever birthed it.
In other words, don't fear buying a house brand of ATF+4 versus a name brand - there will be negligible quality difference between almost all brands of it. I have done one full fluid and filter change on my NAG1 and probably 8-10 drain & fills since (~2.5 qts at a time). At different times I have used all the various house brands of ATF+4 available locally, and even mixed and matched at will while doing the drain & fills. I have had
no problems whatsoever, and the transmission is still going strong despite the regular and unnecessary abuse I give it each and every day.
I'm putting 3500 miles a month on it, and they are not easy miles by anyone's definition. The local climate is a killer, and you would think the transmission insulted my mother with how I treat it. Yet, no slipping, no flaring, no nothing but firm and predictable shifts, even at > 125K miles.
All anecdotal evidence, yes. But in the absence of anything else, why not give it some consideration.
Nuke
PS: on the subject of using the MaxLife ATF in the NAG1: I don't doubt that it will work. However, you will not find anything that says MaxLife is an ATF+4 fluid, despite being good enough for the Mercedes cars these same transmissions also came in. It could be thought of as semantics, but that's a whole 'nother discussion.
My point here is, you can use it and feel secure that nothing bad will happen as a result, but if you're a stickler for specs and try always NOT to run afoul of them - MaxLife isn't a spec'd fluid for the NAG1.
