The upstream A/F sensors are NOT easy to get to on these cars.
I would guess it's more that they can't / don't want to try to change them rather than the sensors actually being seized.
Have them (or whomever you take it to next) remove the front exhaust section (H-pipe) and then they...
Here are the VIN attributes for your car:
HOOD SCOOP:
BLTAB0 : With Hood Scoop
GVW:
AAZBB0 : 4450 LB. GVW
B&A CONTROL CODES ISSUE 030388:
TAPAA5 : Less B&A Control Codes Issue 030388
SALES OFFICES:
AAHAB0 : U.S. Sales
SPRING COIL LEFT FRONT:
TAAU10 : 4R33 5310 FA Left Front...
Unplug injectors one at time while engine is idling and listen for a change in rpm.
If one cylinder has no change you'll know the problem cylinder and can go on to check each component--plug, coil, injector, etc.
I've changed literally hundreds of 3v spark plugs and have seen the occasional...
I just went through the same thing with Lito about a month ago. Thought my speedo might be off after flashing in his tune (it was GPS verified spot on with the previous Bama tune). Lito had me take readings every 10mph of indicated speed on the speedo and GPS speed readings. My car is stock...
If it's not shredded, and you didn't already remove it from the fitting you can reuse it - I've done it lots of times without issue. If you do get a new one (aftermarket should be fine) submerge it in very hot water for a couple minutes, then slowly stretch it by sliding it down a tapered...
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Unless you're going to be putting lots of miles on I'd just leave them.
As a 25+ year tech I've changed countless numbers of these plugs, and extracted countless broken ones too. It doesn't matter much if you do them now or a few years/miles from now -...