There an oil leak coming from my distributor. I replaced the distributor o-ring but that didn't fix the problem. What could it possibly be the problem.

 

There's also a seal inside the distributor, to seal against the rotating shaft itself. If that leaks, it leaks into the body of the distributor, & drips out at the distributor cap. That seal is supposed to be non-replaceable; you have to replace the distributor.

But I've heard of people getting that internal seal... Maybe a search would turn up something. Be very careful damaging the TDC, CKP, & CYP sensors inside the distributor (depending on which year & engine you have).