Need Help
 

I have an '06 GT, manual tranny. I took it in for service and after $500.00 and a day without my car, I got it back with the transmission fluid leaking. At first it was a good amount, and then slowed to about the size of a quarter a day.
Yesterday I took it in again, and they say it is fixed now. I had been told by two other places the whole casing would have to be replaced because the plug was crooked and stripped. I saw the broken thread myself. They have assured me that it will no longer leak, and I was wrong on the stripped threads.
Will vibration loosen the plug? Is it safe? And are they just pulling my chain? Any help will be appreciated. I love my car,and want to make sure it is ok.
Thanks!
Spooky