I don't think a crack in the top of the gas tank or other hole in the tank would cause this problem. The gas tank is under pressure, but only at times, and then only slight pressure caused by the removal of gasoline as the car is driven. However, I think I'd probably replace that tank at some point in the near future... the idea of driving around with an already split tank is a bit petrifying (more likely to split in half in a collision if its already partly there).

The vacuum idea sounds valid, but the question is where?!? I've checked all the hoses in my vehicle repeatedly, and cut off and moved up the ends of ones that were going bad. I do have a slight vacuum loss that I can hear when I shut off the engine... it hisses slightly directly in front of the firewall on the driver's side. However, I think this is off the turbo line since the turbo gauge rides up to the top of the black when the car is off (resting position is bottom of black).

Crud, I don't have a clue. Let me know if you pin it down or think about where it might be happening.

-Rick