Was it just a loose coupling on your cold air intake or your other intake pipes? When I installed my CAI, I didn't tighten the clamps firm enough, and it came loose. I pop the hood and you can see the pipe is not connected around the MAF(mass air sensor). This gives a check engine light and kills the engine, but it is a simple fix you can do yourself. Just put it back on and tighten it well if that is what your problem is. Don't use a screwdriver to tighten these clamps unless you got pretty strong arms. Use a socket wrench (8mm i think) so you can get some good torque on there and be sure it tight enough.
Same thing with your all your intake piping, pipes from turbo to intercooler, intercooler to throttlebody. Those especially need to be tightened well or they can pop off, or leak boost and cause problems.
The turbo gasket thing sounds like BS to me, and I hope they aren't just making s*** up so they can charge you more. It sucks but there are shady mechanics out there that take advantage of people that don't know cars well. It has happened to my parents back when they were paying for repairs on my old car. That's why I try to learn as much as I can and do as much work myself as possible.
Does the turbo gasket on your receipt have a part number? Why was it at the dealer in the first place? What were the symptoms?
