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A rather simple question without too many catches.
Basically if there were a zombie apocalypse and no society beyond smaller tribal-esque communities how long could cars continue to run? (No real concerns on the specific type of vehicle, just that due to the setting it'd have to be an early 2000's model at the latest, so no electric cars or anything.) The story I'm writing is going to broken up into a few parts, each one about a year apart eventually covering 5 years into the apocalypse within a stable enough community that has people with the know-how and general tools for maintenance. Scavenging for replacement parts also wouldn't be too difficult either, given the now very uneven living people to car ratio.
But where I'm caught up is on the required parts that degrade over time such as a car's battery or gasoline which, from what I understand, has a limited shelf-life. How would it take for those or any other substance that degrades over time to be unusable? (Keeping in mind I'm not worried about when it's best by, but when it's still simply functional until)
Thanks in advance!