Originally Posted by
Reptile
A little insight here.
Stock AC Delco isn't what they used to be....literally. GM switched their supplier years ago, and if memory serves me correctly they're Denso on some.
For the older W-bodies, the O2 sensors that had the longer tip, with the long cut vented inlet in them were the best. They read better than the new ones that I refer to the "gun barrel" design simply because they were sensitive enough to read the actual exhaust pulses faster. The aftermarket ones as far as Denso and Bosch don't, and typically throw a P1133 code.
In the end, you just run what you can get. I'm more likely to go to the JY and pocket a used stock one than go fight with warranty at a parts store.