To be honest, I've never had a minute's bother with one, even well beyond 100,000 miles. Very much a "fit and forget" item in my experience. However, the engines do need working hard, periodically. I inherited a 2001 Freelander from my sister. She was going to scrap it, but I needed a tow car. One of the problems was smoke - (boy, did it smoke!) on acceleration. She always hated revving it, never went over 3000, and always drive gently. It has about 150,000 on it at the time. The inlet manifold and EGR were full of oily, sooty gunge, which I scraped out, then washed. It's been fine ever since! Currently being used by my dad, approaching 170,000 miles now.
The very same BMW diesel engine and EGR, as my own and they have always been problematic. Oil from the turbo, is blown up to the EGR, where the very hot exhaust gas, coagulates the oil into a burned on sticky mess, coating the EGR, the manifold and the inlets.