When/Why should you replace the spark plug tubes?

[funlovinguy24]

I was wondering what the determining factor is for replacing the spark plugs tubes. I am about to replace the spark plugs and was wondering if i should replace the tubes as well? Or if i should leave them. There appears to be no leaks on the ground under the motor, would i need to take the coils off to see if there is an oil leak?

What are the tell tale sign to look for to replace the tubes?

Also the Porsche dealer sold me the spark plugs and told me the gap should be correct and not to re-gap them. I asked them if they gapped them and they said they just come that way, and to not drop them and install them. Does this sound correct?

Thanks as always guys