And sensor/rust

So ,quick question.wanted to change the rear right and sensor.came off easy as it was replaced 16months ago with a cheap one from eBay.
Took it out and seen a lot of rust on the sensor and inside the hub.
Bought a h&b sensor and don't want to f**k it up.
Any ideas why the rust?
Thanks

got a pic ?

or do a quick vid onto youtube

Pics.hope it works
https://ibb.co/kAKkvk
https://ibb.co/m6s5vk

I think the hole where the sensor goes in it's a bit large.the guy who took off the old one 18mo ago.drilled it .So I think the small oring that's on the sensor,doesn't seal properly. After replacing the sensor 18mo ago I needed to change the wheel bearing wich was rusted.i am afraid the new one is rusted too

tbh I don't know whether the rust will affect the sensor or not.

If you're concerned about the o-ring letting water in, maybe try plummers tape round it ?

I will take the hub off and see what's inside.can't think on other place that the water is going in.