I bought my car about 7k miles ago and I've been having a problem ever since. When I first got the car shifting wasn't smooth all the time(It's an 04 6MT). Going into second and third is usually ok but 4th, 5th and 6th seemed kind of jagged or notchy when going into gear. So I changed the transmission oil with OEM from the dealer. Now the transmission is smooth only when the car is cold and once i go through the gears and i drive down the street the gears become notch again. A few times as well when it has been cold I would not be able to put my car into Reverse or 1st, it'll stop kinda half way and pop out. Then as of today when I got into my car I let it warm up for a bit im driving and the gears felt weird so I just put it though all the gears while I was slowing to a stop(the clutch was still depressed) and it grinded going into fifth. Any suggestions or possible help would be greatly appreciated. Thanks in advance

 

Syncros can possibly be going bad causing increased wear on the gears. Syncro problems are common on the older 6MTs, Nissan revised the trans in 05/06 to eliminate issues with soft synchronizers and grinding shifts. Look for a CD009 and replace it. Z1 sells a brand new one from Nissan for about $1800. Might be worth it over the headache of trying to find a good used CD009 trans.