Hi all. What can cause a ball joint to fail regularly? I'm now on my third offside front balljoint in less than 2 years, each one has lasted only about 4-5000 miles. When the first one failed so soon I thought it might have been a dodgy part so got it replaced. Now that one has failed it seems obvious there must be some other cause. The mechanics I've been too are replacing it under warranty but haven't been particularly helpful in terms of identifying a cause, just putting it down to "London roads" - speedbumps and potholes. But I drive pretty carefully and don't go offroad or anything, surely the fact that it keeps happening indicates something wrong.

Car is a Renault Clio 1.5 diesel, 10 years old, about 200k miles, standard sort of McPherson strut suspension.