Date registered: Jan 2018
Vehicle: '04 S500 4Matic
Location: Toronto, Canada
Mentioned: 4 Post(s)
Quoted: 44 Post(s)
Sounds like Dave was onto something. The mechanic just phoned. I was correct with it being the front left, but it's not the sensor. He says that the new and old sensors are indicating a missing tooth on the ring, but they are all present.
So it looks like this part will be replaced (not sure if this part is sold separately yet, or part of a bigger assembly). Also a CV boot is leaking so that will be fixed/replaced too.
I hope to have more progress tomorrow.
I will write another update with the final findings. The mechanic has taken photos and screenshots so I will share them too.