Rust on Drive Shaft of Windscreen Wiper

[Wendwell]

I noticed this yesterday as I was cleaning the windcreen. One of the two shafts that turns the windscreen wipers had rust on at least the visible part

I am wondering why and why on only one?

And if anyone else has spotted rust in the same place.

The car, a Trophy Estate, is 17 months old.

 

[Alb]

None on mine but the shaft looks like it's made of an alloy material rather than steel.