……..and one more point regarding S/L shocks, apart from your estimate of costs DG, is that they are not available. I note even as early as 2019 comments on the web mention that.
So standard shocks it is 
My estimated costs IS for standard/non SL parts and labour. Springs and shocks are approximately £100 each side, £200 for both sides. That only leaves £30 for labour, plus VAT. QED they either aren't doing it right, have no idea what they're doing or are looking to take your money without actually doing anything.
The last pair of SL shocks I bought for the Omega was about 14 years ago and they were north of £200 each.
You're correct that they are no longer available, the point is rather that it's not as straightforward as simply fitting standard shocks.
They should know better but either don't care or don't understand what they're doing.
Self leveling shocks are air assisted oil filled. The compressor supplies air pressure to assist the springs by pressurising the outside of the strut body into the rubber boot in order to maintain ride height and is controlled by a level sensor/ECU unit on the right rear trailing arm.
As suggested they look 'wet/shiny' because the metal shock body is constantly being polished by the rubber boot, although they do potentially wear through over time as the boots trap detritus and moisture between the shock body and boot.
After the £320 quote to replace an advisory ball joint, I wouldn't take anything else they say seriously.
And FYI, the Omega front track rods each contain two ends. Each end is a ball joint. So play in a track rod end means play in the ball joint. Ergo you HAVE had them replaced.
