Peter,
Don't know what your model is though, at least for my 92 W124, the shapes of the up and down side are very different, the fit is very tight, I don't think it fits if you flip the cover, plus the hole on one side is much larger than the other.
The mounting mechanism is on the left of the armrest, you have no way to move it to right, you can not reverse the armrest either, unless you want point it for the rear passengers
My up side of the leather cover is also worn, just like many W124s, the decorative strips at the edge are deterioating, it's very annoying, haven't figured out a way to fix it either.