Paul,
Oil was changed recently. Switched to a high viscosity (15w) synthetic blend in an effort to stop a slow leak, but slow leak persists.

 

Doug,
My 04 BMW passed with flying colors + it turns out high heat has destroyed the right o2 sensor and right cat pipe. My question now is whether the defective o2 sensor caused heat to escalate or whether there is another cause of high heat as yet undetected which may fry my new o2 sensors and catalytic converter pipes?

 

What is the fuel trim signature for a failed sensor? Persistently high LTFT?

 

Yep the LTFT will be consistently high on a failed sensor as the reading will indicate a lack of fuel to the ecu and so the ECU will tell the engine to increase the fueling to max.

 

The most likely scenario is that the o2 sensor failed which would make the bank of cylinders run rich which in turn overheated the cat.
If the cat is truly overheated it will be partially clogged or sometimes cracked/broken and you will be down on power also.
For cars failing nox emissions only, I can highly recommend Lucas cleaner, the can says guarantied to reduce nox and it has worked several times for me.