I was checking out a thread that had a picture of a QKLX5M4 X50 Internals and i noticed that my QKLX5M4 internals looked a little bit different.
The horn casting on mine has the letters 'gm' on it and also the '151' component on mine is at an angle, rather than straight. If you look at the bottom along the edge of the circuit board, you'll notice that it has some burrs/rough edges in some spots which the posted pics of the other x50 didnt.
Here are some pictures of my QKLX5M4 x50 opened up. It was built in the 24th week of 2007.