Aircraft storage

How long can an aircraft sit unused before the fuel gums up and contaminates
the fuel system?
For instance, if I leave a motorcycle sit too long without a fuel stabilizer
added to the gas, the gas goes bad after a few months and gums up the carbs.
The entire fuel system is affected after a while. Big problem if you try to
store an automobile without lots of prep since fuel lines and everything can
gum up.
What is the life of av gas before it goes bad?
If it's like white gas it can sit almost indefinately. If it's like auto
fuel it can't sit for long.
I ask because some of these planes seem like they're for sale for over a
year or more, and I wonder what kind of problems they have due to sitting
besides the obvious dry startup with no oil on the cam etc. (as if that
isn't enough of a problem)
Alex



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My 2¢ YMMV