My 190E is lowered. It was like that when I bought it in 2006. It was most likely lowered long before that too. However, its a w201 and uses proper lowering springs.
I've not had any issues with suspension really. Nothing out of the ordinary. I replaced one ball joint and a pair of tie rods since I've owned it. I replaced all the rear suspension linkage, but that was because of age. None of it was in deplorable shape. I also swapped in some adjustable camber arms.
I gather that might be one of the issues in the rear, the camber might be out.
I wasn't aware of the SDL's coming with SLS, I thought that was a 560SEL/SEC only thing? I'm not super familiar with the SDLs though.
Lowering a w126 isnt anything new, just be sure to check out what others have mentioned.
My one friend told me that my lowered and stiffened up suspension-ed 190E takes bumps , pot holes, etc better than his 06 Charger.