I think you are correct in your statement about taking your vehicle to an MB specialist. Compared to todays vehicles the diagnostics are primative. There are a limited number of faults that will cause the CEL to come on and the most common are oxygen sensor failures. The lack of fault memory on these early vehicles makes diagnosis something that is best left to someone who has many years of experience in these vehicles. Seek out a shop in your area that has a technician or two that have been around the block, so to speak. I think in the end you will find that the failure is nothing thats very expensive to repair. Good luck.