i replaced the small bulb for the clock display for my car which is the merc c200-uk model.
the bulbs are not expensive but getting to them could be difficult.
the display unit does come off,apparently it is held in place by clips and a special tool is necessary as per the haynes repair manual.
i managed to remove the offending bulb at the back without removing the steering wheel or display by removing the panels under the dash and approaching from below and behind if you know what i mean-it was tricky,time consuming and frustrating at times,but eventually managed to do it!!
i did borrow a 6 mm socket spanner and fittied this on the back of the faulty bulb and twisted it anti-clockwise -the offending bulb came off and installed a new bulb using the same spanner and turning the bulb clockwise in the socket.
easier said than done-it would be worth getting a haynes manual to tell you how the panels and bulbs come off.