A rock has cracked my headlight lense. Does anyone know if I can replace this by itself or do I need to relace the whole Assy.?

They would like you to think you need the whole assem., but you don't.
The lens is held by 4 plastic clips and one screw [ hidden] on the back side, upper corner.
Capitolwest not only has them in Dot-US version, but there is now a Bosch E code, US version as well .
Just put a set on mine.
There was a dealer TSB on this that is no longer in effect, if anyone is interested...

The original DOT are close to E code and use the DOT/E1 code H4/s [9003].
So if anyone goes with the new Bosch, don't expect a big difference[ although there is a better definition/ right cut-off.]
I have finally made the side by side comparison.
Arthur