Okay heres the deal. I have a 2009 r3 with 32k on it. I've put on 10k miles since may when i purchased the vehicle. The 10k miles have been hard miles. I do drive my car hard. Its a blast to drive. I love the car. My first issue was the 4-5 5-6 sincros were bad. I had a grind going into 5th from 4th and from 6th downshifting to 5th. Mazda rebuilt the transmission under warranty. Turns out they forgot to replace a locking nut. This caused the transmission to pop out of 4th gear basically anytime i was in 4th gear. Mazda rebuilt the transmission a second time about 4 months ago. I'm now having the same issue of popping out of 4th. I'm just curious as to if anyone has had this same issue or any other issues with their transmission. I'm not very happy about having this issue. Honestly i'm beyond furious, I'm going to fight mazda for a new transmission this time around.

 

The same 6 speed transmission is used in the miata, and these transmissions are known to get damaged in mazda's playboy cup cars (miatas). It's generally the 3-4 shift forks that get damaged the most often.

EDIT: I believe that there is a part available from mazda to help prevent damaging the shift forks but I do not know anything about it or even what it's called. Sorry.

 

there is known adjustment correction for this on the S2 manual trans that isn't detailed in the Mazda service manual

NC 6-Speed Transmission Adjustment Procedure DIY - MX-5 Miata Forum