For year 2000 model, some stuff to check for. You can search several of these issues on this forum or at the w210/e320 forum on benzworld.org for more detailed information, recalls, and DIY information:

1. Harmonic Balancer - can develop cracks between 40-50k miles. Not an expensive repair, but can lead to costly damage if let go too long.
2. Motor Mounts - known to wear out on 2000 or earlier models.
3. Rust - very important to look for this. 1997-2000 models have infamous issue with Front Spring Perches rusting out. Big $$ to fix. These are in the wheel wells by the shocks. Also look for rust on top door seals and truck latches.
4. Power Rear Windows - affects all e320s. Bad regulators will go out. Inexpensive fix and several DIY articles to take care of these.
5. Exterior Lights - ride and side light sockets are prone to loose contacts. Drive car with lights on and see if malfunction display lists bad lights. Minor issue.
6. Tranmission Fluid - this is subjective, but conisder getting the tranny fluid and filter changed at 60k, even though Benz says fluid is lifetime. Personally I would do it on a used e320, espeically if previously owned in a large city or if owner was hard on car.
7. Windshield Wiper Gear - pop off wiper cover and make sure mechanism is nicely lubricated.
8. Dashboard - some owners report problems with dashboard cracks. Look it over.
9. Instrument Display - common for pixels to be missing due to bad electrical contacks. Look at clock and shift indicator. Nothing major, but if it bothers you the whole cluster will have to be replaced at @ $1000.
10. A/C - common issue with blower motor. Click on buttons that control fan speed and make sure you can hear the motor increase speed with each level. Also check the rear vents and make sure a decent amount of air is coming out.
11. Battery - Check the Battery area. It's located under the rear seat and can get very cordoded if owners don't use properly vented Battery or neglect to check area.