Hello, I would describe myself as a decent DIY, not a professional mechanic. The only diesel I have ever owned was a Case backhoe, and I had a son-in-law who worked on that for me. SLS = self leveling suspension. OK, that is a feature I did not know about. I want the simplest and most reliable MB diesel model possible (plus turbo) . Is SLS on all w123 and w126's? Thanks, Bill Dukes