2000 Honda Civic small oil leak on bottom half of engine

I've had this car since 2000, and the engine was replaced in 2004. For the first time ever, I've noticed a small leak left in my parking spot. I replace the oil every 3-4000 miles. I notice an accumulation of gunk on the bottom of the motor. I'm hoping that this is a simple gasket problem. Any thoughts? No possibility of cash 4 clunkers? My wife divorced me, took eveything, and left my credit crushed. Therefore, I no longer have any credit cards with which to donate. I am a mailman, and I hope that you can help me.