Sometimes one man's dud is another man's bargain deal!
I picked up a non-operational DDA40X for a sweet deal, took it apart and found the wire broken to the rear motor ~ easy solder repair. Added an extra speaker while in there.
Picked up a non-operational 4-8-8-2 Williams Cab Forward, took apart the tender to see what was wrong and discovered that somebody had modified it with QS-3 and the top board was loose ~ I pressed the board back into the sockets and it now works fine.