Bad catalytic converter?

Hi, I have a Kia Ceed 1,4 petrol 2009. It failed emmission test (CO at elevated rpm). The car has high oil consumption and if i let it idle for a couple minutes a black stain forms on the ground behind the exhaust.

I changed the valve cover gasket (there was oil on top of the spark plugs), the spark plugs and air filter (was dirty which i did not notice before the emission testing). 

I was looking for outher reasons for the failed test and tried checking the catalytic converter using oxygen sensors. Not sure I did it right and if I understand the output correctly. Am I right that the second oxygen sensor has too much movement? Does that mean a bad cat? Also if I change it wouldnt it just get destroyed quickly again by the oil in exhaust?

thanks

 

If the car is fully warmed up, that looks like way more high to low switching at cat o2 sensor in my humble opinion.

IIRC, CO is a rich indicator, no? What are your fuel trims at idle and 2,500 RPM?

There's definitely some abnormal activity in the downstream O2 signal. But, that's not a smoking gun for the cat by itself. The cat temp PID suggests the cat is warmed up, but that's an inferred PID and not an actual reading. The dip in downstream O2 signal at 14:33 makes me wonder about an exhaust leak... What happens to the downstream O2 signal if you jam a rag into the tailpipe?

thank you for your help. I did have a check engine light with a rich code about half a year back but it didnt come back after resetting it

here is the reaction of the o2 sensors to plugging the exhaust - i had the rag in for just a moment just after 12:01:05 and then twice for about 5seconds just after 12:01:25 and 12:02:05
 

here is the trim chart
 
 

what else can I try?

I see you did replace the spark plugs. I would pull them out again and see if any of them have any wet oily deposits on them.