1995 Pontiac Firebird Smoke and Oil Leak

Recently I drove my Firebird for about 3 hours and about half way when I pulled to a light I noticed smoke coming from under the hood and out the passenger side from under the car. I pulled off to check and discovered that it was oil leaking on top of the catalytic converter and exhaust pipe. I check the oil and it had plenty in it so it is a slow leak that seems to only smoke when the exhaust pipe is hot. Could yall please tell me what is leaking because I recently had a o-ring inside the engine replaced and it still seems to leak? Thank you