A rear tail light housing can fail causing the brake light on the affected side to be inoperative. Replacing the failed housing is commonly required to correct this issue.
Car Problem Reports
Mercedes-Benz C230 Brake Lights May Not Operate Due to Failed Rear Tail Light Housings
Mercedes-Benz C230 Problem
Visitor, 1999 Mercedes-Benz C230
Rear right bulb cluster sockets made of plastic. When bulb metal shaft heats up it melts the socket it goes into and makes bulb almost impossible to replace. When it cools it sticks or srinks. 1999 c230