[Bob Ricewasser]

Firstly, I would check the fuse for the top circuit. The switches have also been known to create a problem so you may want to check that. Lastly, try reading the owner's manual as well as search for some U-tube videos on the topic.

 

[Bob Ricewasser]

Turns out I need new front rail guides. Do you know of a site that sells these parts?

You will probably need to order the front rail guides from a dealership parts dept. I would try a Mercedes-Benz dealer first & if they won't order the parts for you, you will have to go to a Mercedes Dealer that sold smart cars.