After sorting the MAF sensor issue, yet another thing is wrong with the car! Pedal judder at low speeds, and BRAKING FAULT/ABS FAULT displaying on MFD. So I took the car to my friend, who had it on the Delphi diagnostics. N/S/F ABS wheel speed sensor implausible, or words to that effect - so he replaced the ABS sensor. After driving it home today, the issue came back. After some research, this lead me to believe it was potentially the reluctor ring. Popped the wheel off to find this:

Would I be right in thinking reluctor ring? And if so, where is the best place to get it, and what size would I need? (2002 - 406 HDi 110 Saloon)
Many thanks

Benjamin