About 2 days after I had my '97 Jetta tuned up, one of the plugs was ejected from the block while driving normally. The threads on the plug weren't damaged nor were the threads in the block. I figured the mechanic neglected to torque the plug properly. I reinstalled it and everything seemed to be OK; that was a little over a year ago. The same thing just happened again. Can anyone render an opinion of what's causing this to happen?
Thanks
John