There should be a "best used before" date stamped on inner tube patch kits. I found two kits that the vulcanizing fluid was dried up even though it had never been opened (glad I also carry a spare tube on rides). Plus, the patches seem to get hard after awhile, though I'm not sure if that matters or not. Putting a date on them would help because then I could periodically check and throw them away when they "expire".
//edited to change "rubber cement" to "vulcanizing fluid" as they are apparently not the same thing
//edited to change "rubber cement" to "vulcanizing fluid" as they are apparently not the same thing
