The lamps in the center console are fed via fiber optics from a bulb behind the Heat/air pushbutton assembly. The safest thing to do is to have a qualified tech replace it. If you want to try, remove the ash tray, and radio, then the 2 screws at the bottom edge of the wood. Carefully slide out the pushbutton assembly/wood panel. Look straight back in the center of the hole you just opened for what could be described as an octopuss like cluster of wires (fiber optic cables actually), in the center is the bulb, replace it and don't forget to test it before you put it back together. Good Luck
As for the 5000 mile journey across country on the same oil, in my opinion the oil in diesels should be changed every 3000 miles. The ash content and by products from the combustion of diesel fuel is high and the filter can only handle so much. As always keep checking the oil level at every fuel stop and have a good trip.
14 year MB tech
7 year shop foreman @ independent MB/Volvo shop