Fluid. My car was originally hard to shift when cold. I went ahead and did what a few others have. Replaced the MT tranny fluid with Amsoil or Redline MT90 (mixed). I only used Amsoil 75w90 2000 Series myself. It made it shift much easier, but I noticed the grinding much easier as well. Over the past 1000 miles with it in there, it has gotten much worse to the point where I was gonna have to take it in. Grinding all the time when it was cold from 1-2. Sometimes when warm. I ordered some 75-85 MT6 stock tranny fluid for a 350z (same stuff that was in ours, but cheaper at Nissan) to put back in. After putting it back in I drove it a little bit and parked. I noticed a difference already with how the car shifted. No notcyness. Interesting. I drove later about 15 miles to do a run, and the car shifted crisp and smooth. No more grinding. The test would be Monday morning. I drove to work this morning, had NO GRINDS 1-2 when it was cold. IT was weird not feeling them.

This car is extremly sensitive to what you put in the tranny. I just recommend leaving it alone and change the fluid every 30k with factory stuff to keep it good.

And Amsoil would have been better, but oh well