jrc

I am not mechanically inclined. I have a 2004 rx8 with a lot of miles from which I put on it....85k. My clutch was getting pretty soft and it was making a low thumping sound putting it into first gear. I took my car into the dealership and had the clutch replaced. With the new clutch it was sticking occasionally trying to put it in various gears. Not a prolonged stick, but a quick pause while downshifting or upshifting. Within a week afterwards, at 5-7k rpms upshifting to forth gear I experienced an intermittent grinding. It also kept a similar thumping noise it had going into first gear...is this normal? Then within about of month of having these symptoms one day even downshifting to 2nd going 20 mph the clutch managed to grind. I then take it back to the dealership and they tell me it isn't the clutch, it's the "synchros" within the transmission. I find it hard to believe a strong coincidence like had happened. I then take the manager for a ride in my car and the car did not have any grinding. I'm guessing this is because it was a fairly warm day because the car has been driven at night and the early morning where temperatures range from 40-60 degrees F, but this is just my own uneducated assumption. All of this work was done at John Hine, Temecula Mazda in CA.
I personally think that this problem is related to the previous work they had done on my car. Please help me out guys.