I have a '93 945 that failed emissions testing.

-------------------25/25 Test----------------------50/50 Test
---------------Reading--Allowed--Result--------Reading--Allowed---Result
HC ppm-------97-------137------Pass----------82-------141-------Pass
CO%----------0.44-----0.76-----Pass----------0.38-----0.79------Pass
NOx ppm-----2043-----984------Fail-----------1932-----1088------Fail
RPM----------2334-----3000-----Max----------1864-----3000------Max
CO+CO2%---14.66----6.0-------Min-----------14.64----6.0--------Min

My questions are (so far) :
1. What is(are) the most likely cause(s) of this issue?
2. Would two exhaust leaks aft cat at the first clamp and a crack at the back near the bottom of the front silencer(1378341) be factors for these readings to be so high?
3. ?(More questions to follow later.)

I have already checked for leaks (Using the tried and true method of a vacuum and an incense stick.) and tuned her up. I found no leaks before the cat. What should be next? Any insight, answers, or help provided is appreciated. Thank you.

I forgot to mention that this is a Rex Regina...]

High NOX can also be caused by lean conditions. If you have a non-turbo, look for intake manifold gasket or intake hose leaks.

So, the catalytic converter is fine? Because I was PB'ing the bolts on it and on the aft cat clamp so that I could remove it in a few hours. I will have to get another sealing ring from the dealer (after I clean up all of the rust) to put it back together. I already have another catalytic converter(Bosal 099-942) at the ready. I placed an order for another O2 sensor already(NGK 25002).

oxygen sensor