Sounds like your installer was a dimwit. If they damaged your shift knob, make them replace it. When you say synchronization, is it inside the transmission? If so, try Redline as suggested. Or are you having trouble finding the gear with the shift knob? There is a block off plate for reverse that can be installed improperly, making 5th and 6th difficult or even impossible to engage. Also, the shifter assembly can be damaged if you don't secure it with a wrench when removing the shift knob. If it's messed up, you may have to replace it - I have one, so PM me if you end up needing it.
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2011 370Z 6MT Sport Gun Metallic | ARC | CJM | Ecutek | FI | Fujimura | R2C | SPL | Stillen | TWM | Z1 | ZSpeed | |