transmission rebuild...intermediate plate specs

[noradiator]

I have a 1970 911 S Coupe. Last year, 3,000 miles ago, I heard a grinding noise coming out of first gear. I took the car to a reputable mechanic for a trans. rebuild. He stated the intermeadiate plate bearing, along with all the synchros needed replacement. I told him to fix whatever it needed.
Approx. one month ago, the noise came back. I went back to the mechanic, saw the tear down. He showed me the bearings, still looking new. He stated the intermeadiate plate was worn, causing the noise. He also showed me the fifth gear had burrs on it.
My question is, should the plate have been measured to see if it was going to wear out with just 3,000 miles.
Do burrs on the gear appear after 3,000 miles also. Or did he just miss these.?
How much do you think I am responsible for paying. I will pay for parts only. He is responsible for all labor.
I pick up the car tomorrow.