bad filler neck kills engine?

Recently my 1999 A-6 went back into the shop due to its engine refusing to remain running. This is the second time in one month, the first time the oxygen sensors were replaced by a shop that was virtually clueless.
They trouble shot for over a week. I referred to that in another thread, since they failed to return the parts as requested. (very little they told me made any sense, but they had my car - and at the time, it wouldn't run)
Now the current work, with a different dealership shop: It seems that a fuel tank emissions vent, that contains a charcoal filter, is somehow getting soaked with fuel.
(both episodes of stalling happened immediately after I filled the tank with gas. I do not top off; I let the nozzle shut off one time only)
When they dry out the vent filter canister, the car runs fine. When they refill the tank, the charcoal gets soaked and the car will not run.
The dealership recommends replacing the filler neck, and they say that the Audi engineers recommended replacing the charcoal canister and check valve also.
If they get in there and see a loose connection on the filler neck, or similar, I'm assured it will be corrected and not replaced entirely, though the fuel soaked valve and charcoal will still be replaced as per Audi's recommendation.
Any experiences with this? I'm told this would cause the oxygen sensors to fail, or shut down the engine, which was the last "fix" - though temporary.
I can't say I've ever heard of a structural failure in a filler neck. The car has not been in a collision.
Thanks,
Grover
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