I have a 2002 Ford Escape 3

I have a 2002 Ford Escape 3.0 v6. A few weeks ago I began to have a misfire on my #5 cylinder and it began to skip. I had the spark plug replaced and at that time the mechanic showed me that I had a valve cover gasket leak. There was also oil on the spark plug. I took it back a few days ago and had the valve cover and intake gasket replaced. The mechanic informed that the car was skipping worse now and that it was up to me weather I wanted to take the car or have him to look into it further. Well I picked up the car and just as he said the problem did not get better and cut off on me. The mechanic had it towed back in and stated that he found another leak around the throttle body that needed to be fixed, but that he could not gaurantee that this would fix the problem. In other words the leak had to be fixed before he could tell if anything else was wrong. I had my car towed to another shop. I was told at this shop that my spark pug coils #4, 5 and 6 were not in correct order and that it had caused my converter to go bad. I guess my question is this. Could the coils being on wrong have caused my converter to go bad after driving a few miles or was the converter already bad? Thanks for your help