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Finally got around to changing it out Memorial Day.
Specimen: 2007 Z4M Roadster, ~33,000 miles. Backroad driver and 2 track days.
Mods: Remus Muffler, AFE midpipe, CDV Delete
Eng oil: LM 10W60
Diff fluid: Redline 75W140
Trans Fluid: OE to Ford Motorcraft XT-M5-QS ~1.8qts
Price: Ford Motorcraft XT-M5-QS Full Syn ~$25-$30 a quart
Got specimen jacked up level and steady, OE trans fluid coming out had a gray-ish tint to it as expected, nothing crazy.
Pumped in 1.8 quarts of Motorcraft full syn fluid, golden/amber color, no strong odors.
Initial drive impressions: With stock shifter/knob. All synchros engage slightly faster. Shift to 1 from stop is easier. 1-2 is slightly smoother (still notchy). 2-3, 3-4, 4-5 & 5-6 are smooth as they always has been. The synchros sync up slightly faster, when delay shifting or downshifting without rev matching (not as good as RP Synchromax, though). Rev-matched shifts are perfect for me (depends on how good you are at them).
Conclusion: I have filled RP Synchromax on my other higher mileage Z4M and I really liked it. Significant difference in synchro engagement. I was not disappointed upon initial drive, I liked the way it performed. However, I still like RP SM. For me still the champion, as it already is amongst our community. This Motorcraft fluid is better than OE fluid for sure, I'll have to drive it more and test it out on upcoming track day for further updates. I feel it will perform just fine. Last track day I had one instance of 3rd and 4th gear grind (maybe clutch not depressed enough or released prematurely).
I was expecting a night and day difference with this fluid like all the Miata maniacs rave about, but, I've come to realize Miata factory fluid is just crappy, changing it to a good quality fluid like Motorcraft results in significant positive change.
Updates to follow. Would recommend the Motorcraft fluid if anyone wants to try
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