'86 300SDL

I would appreciate it if someone could enlighten me on how the indicator lamps located behind the rocker switches on the veritcal area of the center console are accessed. All of the indicator lamps for the top row of switches and two for the second row are out.

Secondly, I would like to hear what some opinions are concerning the longevity of engine oil when highway driving approaches 100%. I intend to take a 5000 mile trip across the country and back in the next week and currently have 1000 miles on the most recent oil change. On a gasoline engine, I would not think twice about 6000 highway miles on an oil change but, I am ignorant of the toll diesel engines exact upon their oil. Any information would be appreciated.