Chris,
as there is no reply I'll say something just so you know that you're not talking to yourself
A few years ago I had the same advisory notice, so i did what we all do, and sought a new rack for a cheap price....
.... I was lucky enough to grab one from the original aftersales clearance for £125 (even though it was a few years after I'd originally bought it for Dico - he was just keeping it warm in his shed until he sold the car

)
I never got round to fitting it, and the matter wasn't mentioned at the next MOT (or any year since).
I still intend to fit the S2 rack when i get round to it, so I'm not offering it to you (or anyone else for that matter!). However, the original MOT guy stated that the ends are purely a ball & socket joint with a peined-over flange, so it may well be possible to slide the gaiter away from the rack and tighten up the housing - either mechanically with a hammer and punch, or if it's screwed in, maybe a spacer washer....
I don't know how much fluid/grease may escape, or if it is easy to do in situ - but it's got to be worth a look as removal of the rack, whilst straightforward, is quite fiddly and time consuming.
If they need replacing, I would suggest that any steering rack refurb place will be able to match them - after all, it's only a bit of threaded bar with a ball on the end - probably not from a part number, but if they can see one on the counter, it shouldn't be difficult.