[SEO9C1]

...The rear exhaust bolt is broken off, has been since I got the car 7 years ago, no indication that it has been leaking, no black carbon tracks, no ticking hot or cold.

Even though you don't see anything visible and this thread doesn't really mention what the issues are, I'm assuming you answered your own question w/ the above. That bolt needs to be replaced.

As for plugs, I run autolite iridiums. Switched to iridium after i saw a couple of platinum tips from delco double plats completely gone upon plug swap. Don't want that stuff banging around in the cylinder and the gap is WAY off once the tip becomes dislodged.

 

[SEO9C1]

Would the after cat O2 going bad cause the rich condition on that side? I thought they didn't do anything as far as engine function. I'm still trying to get the rear manifold bolt out, my little visegrips don't want to hold,,,damn it.

If the rear is bad (or more likely faulty), this tells the PCM the cat isn't there. Since all they do is basically check for the cat, I'd guess that O2 might be salvageable w/ some cleanup or it may even be a wiring connectivity issue.

You've probably read, but many swap good, used O2's into the rears and save the new ones for up front where they're actually reading and sending O2 values.

I may even have a good, used O2 laying around. PM me and I can send it to you if desired.

For the bolt, use a propane or MAPP torch to heat the bolt and spray w/ penetrating oil.

Have even heard of people using heat to clean carbon off of used O2's, but have never done this. I'm OBD1, so if the sensors go bad, they just get new (which is why I've 1 or 2 used ones laying around).