To the OP:
How much did it end up costing you to fix/replace the exhaust valves? I assume they replaced all of them?
I Have 96k on my OBXT and am pretty sure I have a burnt valve on my #2 cyl. 85lbs compression that does not change when you add some oil into the cyl and redo a compression test. Bone stock '05. The original owner was meticulous with maintanence and I have all records. He brought it to the dealer at 86k for a check engine light, it was the cyl. 2 misfire. They put BG 44k (fuel inj. cleaner) in the tank and with a note that if it didint' work they would have to take the engine out and determine problem, est. $1900 to fix. I picked it up at 92k. It always idled a little lumpy but then it finally completely dropped #2 cyl at idle and now the car shakes like crazy. I have been thru 1/2 a tank of techron mixed in, and ran seafoam into the brake booster line with no help. I'll post pics when I yank the engine out.
Searching for misfires here and NASIOC does bring up a decent amount of #2 or #4 burnt exhaust valves on higher mileage legacy GT's/OBXT's