Sorry to hear about this and it is indeed pretty weird. Maybe the thief didn't want you spilling fuel all over the road. Maybe he or she was an environmentalist. You can certainly lock the fuel tank flap from your trunk if your vacuum system doesn't work. I never leave any of my vehicles unattended & unlocked. It has always seemed to me like asking for trouble.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL