Thanks. It turns out that it wasn’t actually a problem with the damping, just the adjuster getting stuck. A bit of brute force has it screwing all the way in for full damping now, instead of getting stuck before the damping really kicks in.
I must admit, I’m not a fan of the damping adjuster on these CTD shocks anyway. I often find that moving the CTD lever out on the trail (with gloves on) results in the rebound getting changed inadvertently too. Sometimes getting switched off altogether, which is great fun as I usually only notice when I steam into a rough section and find the back end is skipping all over the show. I’d much prefer to have rebound damping being something that I set with an allen key or something as I hardly ever want to change it on the trail.