16v limited slip diff

What is the typical service interval for the clutch pack in a limited slip diff. I just purchased an 86 2.3-16 with 89,000 miles and when I went to change all the fluids I noticed that the rear wheels spin freely side to side. I changed the fluid using the specified MB limited slip oil and after 2 weeks have seen no improvement. Is this the typical life span of that unit? What if the fluid was not changed on it up until this point? Is 89000 miles a huge number of miles to put on that diff fluid? Thanks for your help.

[mbdoc]

Since it is called a "limited slip" it won't feel much different than an open diff on a lift. The test is what happens under load. If only 1 tire leaves a mark then the clutches are worn. Heat & friction are the componets that lock the clutches up, plus the right fluid. Have only rebuilt 2 limited slips, & had to order parts from Germany. Don't think there are too many problems or most don't repair. Change fluid at least every 30K miles.