Q: I'm thinking of buying a 2002 Mercedes ML500 w/ approx 208k miles. What parts do I possibly need to replace or check?

Hello....used car repair, maintenance, and restoration costs are highly dependent on the actual, as found, condition of the vehicle. To get a reasonably precise estimate, and also to protect yourself in the transaction, I recommend you request a pre-purchase vehicle inspection. That inspection, carried out by a certified Mechanic, dispatched to your location, will give you the data you are seeking. In lieu of an inspection you do have some additional options insofar as data. The National Highway Traffic Safety Administration maintains a database of consumer complaints, official recalls and factory service bulletins for all makes and models, by year. I encourage you to go to the NHTSA website and enter your vehicle’s year, make and model and review the existing reports which will give you an excellent idea of what has been experienced by other owners insofar as faults in your particular vehicle. I would post the text of the reports here, but they are detailed so it will be more practical for you to view them online (it is free). In addition, "Consumer Reports" publishes system by system vehicle reliability data for all years, makes, and models. This data is available free in the library or on-line if you are a paid subscriber. That reliability data will give you an excellent indication of the relative likelihood that key systems on the model (and year) of interest will fail at greater, or lesser, frequency compared to those rates reported for other vehicles. Obviously, what you want to be looking for in that database is an indication that the vehicle "make and model year" is not a "lemon" insofar as reliability. If you are unable to access any of these resources, or desire data of a different type, please do not hesitate for a moment to re-contact YourMechanic and we will assist you further in your attempts to make a wise used vehicle purchase.