Anyone had this advisory before? If so rough costs?
Yes, but not on a seat, cost depends, nothing last time, cleaned the strut and it never came back.
At any rate Probably ok till next year, maybe, unless it's a
cupra or diesel model - I'm guessing it's a front strut? - give it a clean then I'd monitor it and maybe change it if the misting comes back within a couple of weeks. If it doesn't leave it till next mot.
No real idea on cost, probably 30- 120 each depending on if OEM or Genuine Seat, plus fitting , obviously you will need to do both sides