Katie’s reverb has been turning – seemed to have come out of whatever ‘keyhole’ keeps it in a straight line. We’d been blaming it on the main post turning in the seattube but finally noticed the logo on the back was out of line.

Straightened it up, popped it up and down a few times and it *seems* ok but not had this happen before.

It sounds like the top section has come loose and started to unscrew from the post (it’s not supposed to do that). If you’ve done it up again tightly, it may well be OK.

Otherwise, I’d try and wick some strong thread-locker into the joint (where the shiny post meets the cast head) – e.g. Loctite 290. Don’t unscrew it completely, or metalwork and hellish, oily demons will be unleashed with great force.

(where the shiny post meets the cast head).

You mean the saddle clamp? Don’t think so – the shiny post was rotating relative to the section of post in the frame. I thought they ran is some kind of keyhole slot so that wasn’t possible (though I could be thinking of a different make of dropper)

Sounds like the 3 brass locating pins on the shaft have worn which is allowing it to rotate.

You mean the saddle clamp?

Yes – it can look like the post is turning too, but IME, it wasn’t (it really confused me until I spotted this).

The top part of the post is keyed to the lower with 3 brass sliders. I doubt it would be possible to ‘slip’ these without obvious mechanical damage.

Did it turn really smoothly? If so, I’d put money on it being the top that is unscrewing.