A8 D2 3.7 QS change rear spring

I am guessing that this is something I need to get someone else to do, basically my A8 has a broken rear spring which is quiet obvious as the Offside rear is sitting the best part of an inch lower than the Nearside. I only spotted yesterday after filling up that the tyre was almost in the wheel arch compared the other side.

I have identified the currently fitted spring paint codes, but as I'll be getting a pair of used springs I am changing both as the replacements are of a different rating. Why Audi fitted the sport with any of several different spring ratings I dont know.

I'll be trying to get the springs fitted next weekend, when I am in Hertfordshire but am I likely to need anything else. How prone to failure are the spring supports for example, I might get the breakers to supply these as well. Also how many hours labour will I be looking at, seems a simple job so someone with the right tools could do it in an hour for both sides?.