I know a LSD was standard on 560SEL and 190E 2.3 16V in '88, but I don't know about the 560SL though it seems logical it would have had a LSD standard.

Jack up one rear wheel with the car on a level surface. DOUBLE CHOCK THE DIAGONALLY OPPOSITE FRONT WHEEL!!! Now place the trans in neutral and release the parking brake.

Use a torque wrench and turning a lug nut clockwise, determine how much torque it takes to break the wheel loose and rotate. Be sure you chock the opposite front wheel or you could drive the car off the jack!

A healthy clutch pack should probably be at least 40 lb-ft. The preload is reduced as the clutches wear.

If the breakaway torque is essentially too low to measure with a 150 lb-ft torque wrench, it is probably an open diff.

LSDs can allow one wheel to spin freely - usually with a sudden torque application with significantly different traction coefficients on the drive wheels - like one on ice and the other on dry pavement, and this will rapidly wear the clutch pack. They work best when they are gradually loaded, especially when the is a large difference in wheel traction.

Duke