This is owner caused. No metal can resist sea salt for long without signs of corrosion. You will not be covered under any warranty in regards to this.
Repaint it and coat with lanolin or fish oil prior to use near salt.
It would likely be caused by a worn shock.
Pedders is generally an expensive option. I personally prefer KYB, but any reasonably good quality shock will be fine.
I went with an Opposite Lock step/towbar. You could sell your genuine one.
Alternatively, any fabrication shop can make one and you could get it powdercoated to suit your needs.