If you get to the point you are going to make an offer, it's a good idea to spend a little and get a pre-purchase inspection. Take it to an independent shop that really knows the MB diesels. A mistake on the purchase of a MB diesel can be very expensive. Compression, Compression, Compression. I bought one in the past with low compression. Was okay in a warm climate but when I moved to a cold climate area, the car was history and that was a $3000 loss to me.

In my opinion, it's worth $150 or so for an inspection, especially if you are not real familiar with these cars. The information from the inspection can probably give you some good points in order to negotiate a lower price, if issues are found, which they usually are. You'll know the cost estimate of any repairs needed and can ask for a lower price on the car, or at least know what you are getting into.
Just my opinions, good luck.