There is an o-ring where the distributor mounts to the engine and leaks there are quite common, I believe there is also an o-ring in the distributor itself.
Learn how to set the ignition timing - search there are many threads - before removing the distributor, and be sure to turn the engine to line up the timing marks, and then mark the distributor position AND the rotor position, before disassembling anything, it'll make the reassembly go a lot easier.