z18 primary drive motor bad ?

We have a z18 that will not feed filament - when changing to new filament, filament extrudes if we push down slightly on filament going into the head, but when pressure is stopped, the machine does not extrude. We purchased two new smart extruders last week and have tried both of those thinking one might be a lemon, but with both heads we get the same result of no filament being moved through extruder head.

The printer was purchased in mid October 2015, and we have around 300 hours print time on the machine.
Could the drive motor the smart extruder is affixed to be bad ?

Howdy
What is going in with pulley? Does it rotate at all or not?
Motor itself doesn't fail just like that.
I would take a look at rotational parts, if they are tighten properly.
There is a little black screw on it and this one gets loose occasionaly.

I have a similar problem with my z18. Filament drive motor has no power, it just oscillates and doesn't turn under its own power. I have less then 50 hours on the machine but I have been using the heated chamber feature. Anyone have any thoughts?