I rang my local honda service centre to try and get some more information on the rack guide adjustment... so it appears as though, for at least this service centre, they have never adjusted one. In fact, they've only ever replaced one rack in the last 5 years on a CL9. Apparently not a very common item to have an issue with. He said more commonly there are issues with lower control arm bushes (checked mine already), struts, and engine and transmission mounts. I wont totally discount the rack yet, but obviously it's the hardest job of them all, so I'll give the control arm bushes another check, and suss out the condition of the engine and transmission mounts this weekend. Hopefully the more time I spend under there, the more likely I'll be to discover something. I'll keep updating this post with further information as it comes to hand, but any experiences from members would be gladly appreciated.