Could be a broken spring. Sounds daft, but measure them or count the coils. Sometimes they can break and the piece can drop out on the road, leaving the broken end sitting on its seat and looking OK at first glance.
I was thinking this at first too. I have had this on my car a few times over the years but its not sounding like it could be this at fault with what he described.
I’m not sure if the 206 is similar to the 106 but I’ve had a broken spring like Graham said (clunking during slower turning but not really affecting the ride)
I’ve had Ball joint probs – worn but not really feeling like they affected the ride like you talked about either.
drop links were replaced but only to freshen everything up.
I’ve had a few pugs and even with high miles, never had probs with arb’s.
If it’s the same setup as a 106 gti then the struts are a pain to remove compared to the struts in my Seat Ibiza. There’s more faff and harder to do in ‘the garden’. It’s a lot easier to pull a driveshaft out of the pug too (not what you really want). Once they are off,the spring removal is easy but the nut at the top of the strut to remove the damper is a specialist tool ,although a rough back alley garage would whip them off with some make-do wrench. It removes them but it marks the nut.
If you want to tackle it yourself and haven’t bought spring compression tools etc.. I would probably pay for someone to have a look at it first. It might not cost as much as you’d expect and it’ll save disrupting stuff that might be running perfectly.
Sometimes the home mechanic/I can do it myself approach wastes time and money.. leaving you with a sore head (with pugs) ;O)