Can’t help you much on the part number but if you’re determined to go down the Genuine route and want an S-Line spring you’ll need to match the colour marks on the existing spring as they’re factory marked.
A few months ago (sick of the harsh and crashy ride of my own car ) I purchased 4 x Bilstein B4 shocks and an Eibach Pro-kit set of springs with the plan of fitting them this Spring.
This would supposedly would give me the same ride height as the factory S-Line suspension with a much more compliant ride.
Fate forced my hand last week and as part of checks for an impending MOT I discovered both rear springs had broken ends!
I therefore changed the rear springs and shocks (have yet to do the front, that’s a job for a few weeks time) but I can definitely tell a difference, the harshness has gone from the rear end.
I’d definitely recommend ditching the S-Line springs , the set of 4 Eibach ones only cost about £130.
For reference, here’s a pic of my broken rear S-Line springs showing the colour marking....