You can pull the manifold heat shield off to check for a crack. They ALL crack eventually, my '01 manifolds were cracked at 65K miles. I don't remember what code mine threw, but i don't think it was the same one your getting.
I will check this. Did you hear an exhaust tick to clue you in on the crack or was it just a code that indicated the leak? Once you got the code was the crack obvious? I was planning to SeaFoam the rig in the next little bit. Any leaks should light up with smoke from the SeaFoam. At least this was a good check to find exhaust leaks on the Firebird. (It would roast the cheap manifold gaskets in no time.) Seems we were always looking for a leak. We had to switch over to thicker "header" gaskets and then it was golden...
I had a mechanic checking the Sport out and he never mentioned finding a leak. Though I did not tell him to check while he had it.
And yes I trust him to not be trying to get a $$$ repair. Only guy I know who did not charge me for a repair when he screwed up and misdiagnosed. It was a leaking transmission. He had me do a pan gasket first and it still leaked. I can't tell you how many hours he wasted trying to track the leak. It continued and had him and his tranny friend stumped. They knew it was trying to overheat, but why? They were thinking it needs a aux trans cooler.
In the end, I figured it out thanks to google. Ended up it was a plugged tranny vent and the fluid was coming up the dipstick. He unclogged the vent cleaned up the rig and charged me nada... Most places would still charge you a diagnostic fee and a time for the cleaning of the vent... I'm not sore about the forced tranny pan gasket, as it really needed a trans service to verify all was well inside after my daughters boyfriend got it stuck in 3 feet of mud. (hense the clogged vent)
