mof - I have exactly the same issue, but I do not know whether the key that the previous owner broke off in the back box lock is the correct key! In my case, he provided two "keys" with the machine, one broken stub (which I later found the rest of inside the back box lock), and the other a full key that fits the coin box lock. The number printed on the key heads of both are the same. Personally, I have never seen a machine with the same lock on both the coin box and the back box, so I'm thinking someone THOUGHT the key should fit, but it didn't, and it got stuck, and the key broke. I am telling you this because in my case, the broken part of the key (with the teeth) may not come out as yours did. But I would like to try what you did. However I do not understand the steps you documented.
The video posted by 27dnast doesn't play for me either in his posting above nor if I go to the video in YouTube (video just "spins"; never starts playing). And the transcript of the video is just AWFUL... the guy starts and stops and never really explains well in words. So ALL I have to go with is what you documented above, in your post.
Here is what you posted, along with my questions:
1) touch of WD40 > cuticle nail cutters > removed key
(I think I understand this step... spray a bit of WD40 or silicone spray in the keyhole, and try to work the broken part of the key out with something like nail cutters, tweezers, etc. Not sure this will work for me if it is the wrong key and is jammed in there, but I will try.)
2) shoved the key in all the way
(Okay, at this point you have the broken key out. Are you taking that broken part and shoving it BACK into the keyhole?? Or do you have another (good) key and are shoving it into the keyhole?)
3) took pliers reverse and wedged them in like a wide screw driver
(I have no idea what you mean by "pliers reverse and wedged them in like a screwdriver". Pliers are quite wide. And if the broken key is already in the slot, how was there any room to "wedge pliers in like a screwdriver"? Are you using needle-nose pliers at this point? Even so, with the broken key taking up the only space in the keyhole, where are you wedging the pliers into... and what do you mean by "reverse"??)
4) practiced on my Taxi a few times until I was ready
5) Open SAYS-A-ME !!!
6) Removed key
(If this was the broken key that is back in the lock, how did you get it back out this time? Seems it may have been even further into the key slot than it was the first time?)
In my case, since it MAY not even be the correct key that has broken off inside the lock, I am not even sure I will be able to pull it out, even after using silicone spray. I will try tonight. If I can't, I may have to resort to drilling (into the broken key AND the lock cylinder). And even then, I am not sure of what may happen. (I just drilled a coin box lock on another machine this morning, and the lock STILL won't turn! I am debating about continuing to drill into the lock and into the screw in the back of the lock that holds the locking "bar".) In this case, drilling it could be catastrophic, because the lock is in the top of the back box, and I have no idea whether the back of the lock is attached to a rod or other mechanism that may fall apart, and then I will have a broken lock and still not be able to get into the back box... then what?? This is not like a coin box lock, where the lock simply secures the door from being opened. In this case, the lock is nowhere near "something" that may swing open. So, turning the lock MUST pull on a rod or something, and if that link between the lock and the rod is severed or drops off, I will be in real trouble!
(Thanks, if you can expand on your list of what you did!)