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I know the AX15 and many other transmissions that have soft metal synchronizers that do not like the new GL-5 crap. I personally fought between the Pennzoil Syncromesh and the Redline MT-90. I can't comment on the MT-90 although I have heard good reviews, but I can say the Syncromesh works wonders. My recent 91' YJ purchase was a good deal due to the fact that you basically had to grind into gear; and the owner knew little about the mechanics. I replaced the clutch and slave and still had some rough shifting. I replaced the fluid with Syncromesh and, although the syncros are basically shot, there is a night and day difference. I can now shift without a grind at all! Second gear is usually tough to get into but I don't hear metal 
The conditions have only improved over time and its still winter. I would highly recommend it for shifting issues.
The conditions have only improved over time and its still winter. I would highly recommend it for shifting issues.