Is my Catalytic converter bad?

I have a 2000 ford Taurus with 197,000 miles on it, I first had a small leak near the oil pan of my engine that grew larger and would cause smoke from flinging back onto my converter. I cleaned the engine and let it dry for a few days and made sure all electric parts were dried out. However, after starting my car it started to make a whistling noise and ran very rough with the whole engine shaking in the process. When I tried to drive it, it had no power at all, it barely went 10 mph even when I held down the gas peddle but the engine wouldn't really rev when I held the peddle down all the way, when it was in gear. Also, going up a hill the car practically went backwards and had 0 power. I hooked up a code reader and it said that there were misfires in my cylinders, but the next day it read no misfires. I had a friend look at it and he tested the heat on the converter and it was really hot on one side and cold on the other, and there was very little coming out of the exhaust pipe. A new Catalytic converter is very expensive and i don't want to fix something that doesn't need fixing, please help.

First off get that oil leak fixed.Secondly when it comes to codes popping up and going away I IMMEDIATELY fix whatever problem it was. I don't care if the light goes away for a few months then comes on again cause for all you know whatever set off the CEL might be catastrophic next time around. If its misfiring then either change wires, spark plugs or coilpacks(If you have coil packs that is).

Fords really are famous for rusty rotted oil pans. Get yours replaced before all the oil runs out of the engine one of these days. New bolt on direct replacement Walker Converters are NOT expensive.