This is very interesting- Stern posted a documentary about their business today, and there is a scene where it quickly shows two Slimer mechanisms being play tested on a whiteboard type of setup.
You will notice one mechanism resembles the one shipping on newer Pro's and also the LE's - and the other one (right of picture) is the one that has hit registering issues.
I am wondering if Stern had a bunch of the bad ones made and didn't want to junk them, along with playfields with typos, in order to save a few bucks. I don't understand why there was play testing of two separate mechanisms, and they shipped with one version for a few weeks then switched to the other, especially when most people were saying the original one doesn't register shots properly unless rigging them up with washers and other tricks.
Could it be that the initial shipments of Pro's were Prototype machines Stern sold that really were not the final design? I hope not..
Newer / better working design on Left side, older/original "tempermental" design on right that initially shipped on Pros: