my car has rear disc brakes, but how do I know it has lsd. its an 81.

or another easy way to tell is to put your car on jack and spin the wheels with your hands and if both tires spin the same way then you have LSD

That's called an oil leak. :nod:

If I remember correctly, the lsd should be able to bolt right in, in place of the old diff. It is possible then that the p/o put in a lsd. On my car, however, they swapped the entire rear axle.

for a transmission? do a search

rear ends i believe were 3.90 for 12A and most common knowledge would say a 4.10 for the SE, but more accurately 4.08 and some change. i think its in the factory manual or a racing beat catalog.