Can someone elaborate a little on what this component is, what it does, and what problem and which cars it attempts to alleviate? I don't have a 3-4 slip in my car (1990 w124 coupe), but if I do some day, I'd like to know how to go about fixing it and what parts I need.

Thanks,

GregS
'84 300D, 173k
'90 300CE, 163k