The only explanation for the (REAR) pads being worn down are
either a SBC malfunction which may be hard to prove or diagnose
or the ASR function of ESP is kicking in, constantly trying to stop
spining rear wheels. Which is super hard on the pads.
I have seen lots of cars with higher HP or 4-matic in our area
that eat up rear pads during the rainy season in record time.
I had a client with a ML55 that used it for skiing. He did a bunch of snow and ice driving and the ETS was constantly trying to stop those rear wheels from slipping, needless to say we replaced the
rear pads at only 5500 miles.
His rear wheels were much darker from all the dust.
Being that your car has less than 12,000 miles and needs rear pads, If it were on my rack I would attack it as a malfunctioning
If you did drive like a maniac, your front pads would be toast long before the rears.
Driving with the parking brake on would just smoke the parking brake shoes, not the pads.
I would suggest you make NOISE to your MB Center about this issue and request this be fixed as well as replacing the rear brakes no charge.