Stumped on engine misfire?

I have a 1996 Dodge Grand Caravan with the 3.8L engine. In January, the car started to shudder and engine misfired. The ODB II scan read P0305-Cylinder no. 5-Misfire Detected. I replaced all six spark plugs and wires with Bosch Platinum Plugs and Bosch wire set. The car ran fine for two months. The engine then started to misfire again. The OBD II codes read P0352-Ignition Coil no. 2 Primary Circuit and P0300-Random/Multiple Cylinder Misfire Detected. I replaced the ignition coil with a coil from Pepboys and inspected the wiring to the coil. The car still misfires in cylinder 5 and the code P0352 is generated from the computer. I took it to the mechanic. He inspected the plug in cylinder 5 and said it was ok, but it had a little oil on it. He replaced the plug and the car still misfires. He said I should use a coil from the dealer. The dealer told me for the 1996 it did not matter. I tested cylinder 2 and 5 with new wires since they are on the same coil bank. I replaced the O2 sensors in November '06. All vacuum tubes are intact and the fuel injectors and their wiring are fine. The battery and alternator seem fine and I have had no issues with the system grounds. Should I use the dealer coil? Could my problem be the camshaft or crankshaft sensors? Could the problem be electrical? Do you have any suggestions on what I should do?