The mid-late 90s Toyota Camrys were known to sludge up in 20,000 miles. EGR will do that to oil. Toyota paid a hefty price in recalls for this issue. If you are the customer Mercedes has started designing their new lineup for (lease customer who trades every 3 years), then don't worry about it. If you want to own your car for years like Mr Daimler and Mr Benz intended, then I would change it every 5k from day one.