Scanner found Oxygen leak. what causes that?

My engine light is one so my mechanic scanned and found an oxygen leak in the exaust. What can cause that? for the full story read the following
post.
I have a venture van 2000 and recently got an misfire code that was read at the mechanics shop. Also, scanner detected an O2 leek. The cleared the error message and (June 25th) I change the spark plug for that 6th cylinder. I notices the nipple circle on the top hook of the spark plug was totally gone. I checked a different plug and the nipple was fine on that one. Also to mention that we had problems starting the ignition on the first try (sometimes takes 5 tires). Now that I put a new spark plug it starts like a beauty. I had the engine light come up before (5 months ago) and mechanic found a O2 leak. But did not mention a miss fire problem. That time he cleared it and it was fine until a week ago. So now I want to figure out why I had this problem so it does not happen again. My warranty just ran out and will be selling the van this summer. I would appreciate any additional insight as to what the root cause of this problem. Could a miss fire cause O2 leak? Or did the o2 leak caused the miss fire, leading to worn out spark plug? I have about 50,000 km (about 30,000 miles). What do you think? Thanks.
I have driven it some more today and now the engine light is on again, after changing the spark plug.
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replace all the plugs and the o2 sensor get the injectors cleaned

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is O2 and oxygen not the same thing?

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If this is in the US, take it back to the dealer. The emissions warranty is over 36,000 mi (I think it is something like 80,000 mi). Not sure about other countries though. Look in your warranty materials.
Jeff

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