Had an upstream O2 sensor fail on the 2001 Durango last weekend.  Attempted
to do the repair myself and gave up after a few hours.  The O2 sensor was
seized in the exhaust pipe.  600 pounds of torque, torch, nothing would get
it.  

It was also in a difficult spot (on top of the exhaust pipe facing the
bottom of the vehicle).  I have a special tool to remove them in that
situation, but it was stuck.

Took it to the shop for them to do the work.  They were also unable to get
it out.  Felt a bit better about my attempt after I heard that.  

They are going to drill a hole and install a part that basically creates
another O2 sensor hole to screw the new on into.  The only other option was
cutting that section of pipe out, which would have been more costly and
time consuming.  

Several years ago, I replaced the O2 sensor in my Monte Carlo without too
much trouble.  The main difference was the upstream O2 in the Monte is
basically in the engine bay and not on the bottom of the pipe near where
all the rust happens.

- Mark
  
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