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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