The two most common oil leaks come from the oil pan gasket and the oil cooler lines.
To get to all of the oil pan bolts you will have to remove the "K" brackets under the engine mounts. Don't worry, removing the "K" brackets won't cause the motor to drop out of the car. There's about 4 bolts that you just can't get to with them in place.
The oil cooler lines were just a bad design, sooner or later they will weep oil.
There was a thread here recently about them, if yours are original, I'd buy a set now.
http://www.zr1.net/forum/showthread.php?t=19418
'Crabs