If I can recall, this has been a subject of a comprehensive discussion before. Do a search and you'd be pleased with what the archives hold.
For the age of the MB, rust would be a factor to look at. Mechanically, its a good built with very lasting impressions. Compared to your Audi, it would have less electrical problems.
I would think its the usual wear and tear on the bushes, engine mounting, and perhaps do have a check on the belts and engine compression.
126 tailed by a 203, 129 leading the pack.