As I understand, failure mode is leakage due to arcing from ID to OD (fuel/PTFE interface to stainless jacket) causing breakdown of the PTFE. It would take VERY high voltage to break down PTFE. Agree conductivity of the fuel inside is a key question... gas vs ethanol and all mixtures in between ??
Here's a photo of a damage site I found online:
http://www.microlabgallery.com/galle...2040X%202.aspx
Hard for me to believe this is a common occurrence and fuel leaks don't always end in violent explosions but the risk is there I guess.