5th gen manual shift grinding into 2nd

[Slikus Vaw]

I have a 2010 Camaro RS and I am having problems shifting into 2nd while it's in high rev. I just installed a short shifter and it has gotten better but the grinding into 2nd still happens. what can I do to stop it from happening besides not shifting at high rev or waiting for the rev to go down then shift? is it a problem with the transmission? any help is greatly appreciated. I just got this car back in Oct and I love this car and I am going to take great care of it. unfortunately, I got into an accident, someone backed up into me and caused damage and I got it fixed through insurance but the body shop I took it to wasn't as good/professional as I thought and he damaged my vehicle and I noticed my shifting problem got worse after receiving my car back. he denied that he/his works did the damage and refused to replace the cracked dash and he also left my car very dirty after the work was done. I think when he took it to get cleaned(outside) he decided to have fun with it and see what it had and by doing so forced the shift into second not caring if it damaged the gears or not. would changing the transmission fluids help at all?(haven't changed it since i got it around 8k miles) i do drive a lot .

[gsxrturbo]

pretty common,you need second gear replaced and also the carbon cones that they use for synchronizers

[Rock-It Man]

Worn out synchros, as stated above.

After that, why do you need to shift into 2nd at high revs, except on a drag strip?