Step-by-Step Instructions:

Disconnect the Battery:

Before diving in, ensure the battery is disconnected. Remove the cap, disconnect the ground side first, followed by the power.

Undercarriage Panels:

Get under the car and remove the protective panels. Two panels need attention - one at the front and the second one at the back. Utilize an 8mm tool to remove the screws.

Tools Required:

Equip yourself with a variety of tools: a couple of ratchets, 3 and 6-inch extensions, 8mm for panel screws, 10mm and 13mm sockets, and a Milwaukee ratchet for efficiency.

Starter Removal:

Locate Starter:

Identify the starter; a 13mm with a plastic cap and a 10mm for the ground strap.

Disconnect Power:

Remove the plastic cap, exposing a 13mm nut. Disconnect the power line directly connected to the battery. Ensure the battery remains disconnected.

Remove Ground Strap:

Unscrew the 10mm bolt holding the ground strap connected to the starter.

Unclip Harness Protector:

Unclip the harness protector, giving access to the starter screws.

Loosen Starter Bolts:

Use a suitable setup, possibly behind the catalytic converter, to reach and loosen the two starter bolts (13mm each).

Starter Direction:

Ensure the solenoid faces the catalytic converter when pulling the starter out. It can be tricky but persevere.

Reinstallation:

Place the starter back, making sure the sprag/gear faces the flywheel.

Final Steps:

Secure Components:

Ensure the ground wire and power cord are securely attached. Tighten the 10mm and 13mm bolts.

Reassemble Panels:

Put back the protective panels underneath.

Battery Reconnection:

Reconnect the battery, starting with the power side, then the negative.

Initiate Steering Angle Sensor:

Turn the car on in park, rotate the steering wheel from lock to lock, then drive about 100 yards to reinitialize the ABS and ESP systems.

And there you have it! A successful starter replacement on your Mercedes-Benz S550. If you found this guide helpful, stay tuned for more automotive tips. Safe driving!