Son o' Gutz failed the biannual emissions check for the first time in his 19 years (92 245, M247, 245K miles)this week. Performance and mileage seem to be off lately as well so it's time to look into things. Just checking here for the collective wisdom in case I've missed any obvious cues.

Specifically, readings were:
HC 1.69 ppm vs 1.00 limit
CO 10.3 ppm vs. 12.0 limit
NOx 3.97 ppm vs. 2.5 limit

For the preceding decade, the readings averaged well within spec with little variation:
HC 0.46
CO 4.7
NOx 1.43

So although HC and NOx are over the limit, the CO has doubled as well.

I'll look for the obvious things like vacuum leaks and ignition components, but I'm also wondering if the cat has just completed its 9th life and it's time for a replacement. O2 sensor was recently replaced and was reading well a month ago, and no codes have been thrown.

Thoughts and comments?