833 4spd repair advice

Got my 833 4spd trans rebuilt, and I installed about 6 months ago. I have never driven the car only started the motor a few times with trans in neutral .."always."
Recently sent car to go get an entire once over, (nuts bolt brakes fluids) as this was my first build ever.
The shop called me to tell me my transmission is shot due to my starting the engine a few times. I had no idea that I could have damaged my manual trans as long as I had in neutral but apparently I was sadly mistaken.

Question is, any guesses as to how much damage I could have done here? Are we talking I need a whole new rebuild? or..?
Any help is appreciated