I changed just the driver side, front sensor. These are very hard to get out! I thought about trying it ... but was tired. The old one didn't look awfully dirty.... the reason I did that side is because I got suckered into having it "looked at" for 50 bucks that turned into a 125 bucks and all he told me is that the driver speed sensor is out. Yes, serves me right, I thought this mechanic would know better and had the equipment .... nah! It's tough finding a trustworthy person.
With winter rapidily approaching - I need the ABS to work - - I will try to give it another go - or I will take it into the Benz dealership and get fleeced willingly!
Sorry, I am complaining, I am tired and frustrated!