I got a brand NEW mower from WM. "Out of the box" the drive didn't work.
As it is a 2 hour round trip back to the store, I investigated it myself and
found that the outside portion of the drive control cable wasn't properly
install and had gotten loose from the frame. I "fixed" it with one of
those plastic wire ties used for bundling electric wires.
There isn't much to these drive systems: just a belt to the "transmission"
and something you control that changes the tension on the belt.