SLK Rear Brake Pad Change
All SLK rear brakes are similar. Here is an oveview.
I used Porterfield Pads for there low dust properties.

First loosen the fluid cap.

Above is an overview of a rear brake caliper.

Simply tap out the pins, the spring will come out.
Pull the pads out. Press the pistons in (one on each side).

Grease the new pads. Spread it with a gloved finger.
Insert the pads with the greased (non friction) side to the pistons.
Reinstall the spring and pins. make sure the pins are fully seated.
Retighten the fluid cap. Press the brake pedal several times to seat the pads.
Drive gently for the first 100-200 miles.