It is most likely the bulb being burned out but if the bulb is good then it may be the fiber optic cable that gets the light from the bulb to the indicator or the plastic unit that the end of the fiber optic cable snaps into. The cable could have popped out or the plastic holder could be broken. In my 1992 300SE, the plastic holder had broken and the replacement piece (MB) was designed to slide onto the shaft in the shifter box. Rather than tear the box apart to get the shaft out, I notched the bottom of the piece so I could snap it onto the shaft and then the pin held it in place securely. Be careful to have the spring loaded plastic piece in the travel groove when reassembling.

Tim