flat machine giving away free product

[Dmkraz]

I have a 2-column A&A flat machine - bought it new 2 years ago.  Some kids figured out that if you don't put any money in, but repeatedly slide the lever back and forth eventually a tattoo comes out.  I opened it up and found that pushing in the lever (without money) until it stops and releasing causes the little square plate to move just slightly and catches the bottom tattoo and moves it a tiny bit towards the slot.  Do that enough times and it works it's way out.

I assume this is a known scenario - what's the standard remedy?  A little wd-40 on the top of the square plate ?