Maybe I overtightened the original headset on my Brompton. I had some play and after fixing it, the added force maybe caused premature wear to the bearings. It is easy to overtighten the headset – this is a job that needs experience, a “feel” for the right torque – but a non pro mechanic has to adjust a headset only once in a year – max – nothing to build up the needed sensitivity.
Anyhow. I had a reason to get a new headset and since I love Chris King headsets (I run one on my Moulton too): that was the place to look for a new one.