do i have a limited slip rear 35?

okay, here's the weenie question of the day: Without opening up the rear end, how do I know if I have a limited slip diff (I didn't want to sound like a lost hippy and ask if I had lsd..) in my new (to ME) 91 limited. It's pretty stock with a 3"skyjacker lift, header, but nothing changed in the original drivetrain. 242, auto, H.P. 30 in front, 35 in back. I just changed the 80-90 in both by pumping out all I could with one of those $5 plastic pumps, and then I filled up with Slick 50 80-90. My previous daily driver had open diff's F & R. Did I ruin my rear, or am I panicked for naught? If I do have a limited slip, what should I do?:explosion

If it hasnt been removed, there should be a tag on the diff cover that says its a LS or says to add friction modifier. If no tag, then jack up the rear of the Jeep and spin one of the tires. If the other spins in the opposite direction, its open.
If it turns out to be a LS, dont forget to add friction modifier to it.

Lots of the synthetics have enough friction modifier in them to not need any additive. If it chatters you need more. But regardless you won't have hurt it.