Yeah I guess ill give it a shot and come back with what I find.

I honestly can't remember how it all hangs together; give it a try, what have you got to lose?

Yes there is a very small pin sized hole in the 11:00 location on one side (as sceen in the picture) and another in the 2:00 possition on the other side.

Would you suggest tapping that pin all the way through the other hole?

I think that I just had an ABBA moment (AhA!)

Could it be that there's a small pin holding it all together at 11:00 / 2:00 from the square hole? 

That's the hard part - I can't remember. 

I think I see whats wrong with it from the picture you gave me.

in the picutre of the tumbler theres "the disc" I was talking about, and in your picture it has a small tab on it, where mine does not.

Now the question is, how do I get the tumbler out of the handle?

I replaced the lock cylinder(s) on my mini some years ago in order that they'd share the same key.  As I recall, the bootlock cylinder was the most difficult to change and I honestly can't recall seeing that small tab as part of the assembly.  It's really hard to tell from the pictures what's going on inside the square hole, but if memory serves, the cylinder has a small circlip at the terminal end - maybe you can find a way to dissassemble it, clean it up and examine it further.

Image Gallery

Here is what I am working with.

1. The first picture with the small tab on the right was found inside the square hole on the handle. When turning the key this tab did not move what so ever.

2. The second picture is hard to see but on the wall of the square hole closest to the handle is a small disc that turns as i turn the key.

3. The third picture is also hard to see, but on the left and right, inside of the square hole are two holes that apear to have nothing in them, even when spinning the key.

I would assume as I spin the key from a 12:00 positions to a 6:00 position that the small tab would move up or down, correct?

As I recall....you should be able to remove the barrel and clean it up.
 Can you turn the key with the boot lid open and the locking tab come up?  If so it would just be a matter of...alignment...or the tab it "locks" onto is bent

Could anyone tell me how the lock for the boot of a Mk3 Mini works? I'm trying to fix mine and im not sure if something is broken or just jammed with gunk.