I've got a Peugeot PX10, I believe it's probably from the early 80's. It's got a Lightrace headset which appears to be in good condition. The threads on the steerer tube are also in good shape, as far as I can tell.
When I try to tighten the headset down, the nut feels like it is all the way tight, but I can still hand tighten and loosen the headset very slightly. It LOOKS like the nut is in full contact, but apparently it is not. This is really frustrating because on rides even that slight bit of looseness makes my headset rattle and changes my handling characteristics.
I'm aware that the headset is (most likely) French sized, which, according to Sheldon Brown's site, means that it is only .2 mm narrower than a standard quill stem. I sanded the stem down, and I'm pretty sure that I got the .2 mm off, but do not know for sure.
Does this problem mean that I need to sand the stem down more, or do you think this is a problem with the headset or something else?