My old keyboard finally died. Kaput, dead, it will be missed.

I've read many good things from coders about the MS Natural Ergonomic Keyboard 4000, but when I went to the store they only had the 7000 bundle (keyboard + mouse). The keyboard looks nearly identical to the 4000 other than being wireless and not having the LED indicators in the "dead zone".

To the point: I'm not sure if my keyboard is defective or needs to "break in". 

My Enter key (above right-shift) is very difficult to use. Prior to making this purchase, I read in several places that the key resistance on the 4000 series is fairly healthy. THe keys feel fairly solid in general and match the "heavy resistance" description. However the Enter key does not work at all unless I hit it perfectly dead-center (and then it works very smoothly). If I hit it slightly to the left or right of center, it sticks and does not go down.

I'm wondering...

1. Are the 7000 and 4000 keyboards essentially the same?
2. Has anyone else had issues with their Enter key / is this a common problem?
3. Is there anything I can do to reduce the friction for better action?

I'm trying to save myself a trip back to the store if this is a common experience for new keyboards in this family....

![MS 7000](https://i.stack.imgur.com/AxCFF.jpg)

*UPDATE:*

Based on Journeyman's answer, I didn't feel comfortable lubing the keyboard myself. I returned it to the store today. Unfortunately they didn't have any of the same model in stock, but they did have the 4000 keyboard available. The keyboard looks nearly identical but feels completely different. My original 7000 purchase must have been poorly assembled, or is simply inferior to the 4000.