I found that the rack was a bit loose, as the small screws holding it needed tightening.
I ended up removing the pressure plate cover that holds down the focuser knob, removed the draw tube and degreased the rack and pinion, away from the tube. It was the usual Chinese glue grease affair. 🙄
Once I had cleaned them up, I put the rack back on the draw tube and screwed it back on.
I regreased the rack and pinion, with small amounts of grease, wiping off the excess.
I put it all back together and it seems to be okay, but I'm unsure how much to retighten the pressure plate too. At the moment, it's just a light pressure, making sure all the screws aren't too loose, incase they fall out.