99 300D I am looking at..need advise

I am looking at buying a 99 300D with 300,000 miles on it. The owner replaced the trans in 2001 (not sure of mileage then). It has many new suspension and steering parts replaced and he says it runs strong and does not leak or burn oil. Supposed to be rust free. Interior in good shape.

Having never worked on or driven a newer diesel is there anything I need to look out for? I am only looking for something quieter on the highway with better mileage than my 83 300SD. Any advise will be appreciated. The asking price on it is $7500.