Trust the sensor, it's got plenty of pad left when it goes off, won't leave you stranded or be unsafe.
Usually when you replace pads, it's a good idea to cut the rotors and the shop doing will mic the rotors and let you know if they will be out of spec after they are done cutting. Personally I look at the rotors and if they are smooth and no warping, I just use some emery cloth to scuff them up front and back. Worst case is they may squeal for the first week or two until the new pads comform to the rotor. If they are warped or grooved, I just buy new rotors, they are pretty cheap, just bought new rear rotors for my kid's SLK, $34 each. Beats paying $15 to cut the old one and wait an hour for them to be done. You way want to consider low dust pads. It believe Hawk makes a ceramic for your year MB. Also, order one sensor even if the old one wasn't tripped because sometimes they are hard to get out and may get damaged removing/inserting them. Get packets of brake grease and antisqueal compound, usually 99 cents. Get a can of brake cleaner spray. You want the surfaces to be free of any grease and believe me, you'll get very dirty doing brakes and that's OK as long as the rotors and pad surfaces are clean.
If you do the rears, take off the rotor and inspect the parking drum brake. A whole new parking brake kit with shoes, springs, etc is cheap $23.
Usually when you replace pads, it's a good idea to cut the rotors and the shop doing will mic the rotors and let you know if they will be out of spec after they are done cutting. Personally I look at the rotors and if they are smooth and no warping, I just use some emery cloth to scuff them up front and back. Worst case is they may squeal for the first week or two until the new pads comform to the rotor. If they are warped or grooved, I just buy new rotors, they are pretty cheap, just bought new rear rotors for my kid's SLK, $34 each. Beats paying $15 to cut the old one and wait an hour for them to be done. You way want to consider low dust pads. It believe Hawk makes a ceramic for your year MB. Also, order one sensor even if the old one wasn't tripped because sometimes they are hard to get out and may get damaged removing/inserting them. Get packets of brake grease and antisqueal compound, usually 99 cents. Get a can of brake cleaner spray. You want the surfaces to be free of any grease and believe me, you'll get very dirty doing brakes and that's OK as long as the rotors and pad surfaces are clean.
If you do the rears, take off the rotor and inspect the parking drum brake. A whole new parking brake kit with shoes, springs, etc is cheap $23.