P0300 and 2002 Jeep Liberty (3.7L)

Hello, I am getting an intermittant P0300 code accompanied with 302/304/306 codes which indicate all of the left hand side cylinders. This past weekend, I pulled out each of the spark plugs, regapped them, and reinstalled them (they are only 1 year old). The spark plug for cylinder 4 was blacker than the others and had a distinctive gasoline smell. As well, I performed a fuel system leak test and there is a fairly significant leak on the fuel rail/fuel injector side of things (pressure goes from 50psi to 30psi in 5 minutes). The symptoms I am experiencing is the car is very slow to start after it has been sitting for 15 minutes or more. It normally takes several turns of the key to get it going. If the car has been sitting for less than 15 minutes, it starts immediately. Strangely, if the car has been sitting for a couple of days or more, it starts right up. As well, on one of these slow starts, there is a very strong gasoline smell from the exhaust when it finally starts up. Recently the car has begun to experience a very slight rough idle. My theory is that there is a leak on injector 4 which explains the pressure drop and the black spark plug. When the car sits for a couple of days, all of the fuel has had time to evaporate so it starts right up. Does my theory sound reasonable? What else could it be? If my theory is reasonable, how can injectors leak? Just through the o-rings? What about through the injector itself? Thanks.