Oil caps... they wear out?

[Skunksmash]

I noticed that my oil cap always had some oil around it. So I pulled it off and it looked a little old and tired. But, I couldn't really see anything wrong with it that would cause it to barely leak. So I went and bought a new one, that came with a rubber seal that is probably 10-15 times thicker than the one that was on there. Seems to seal up much better. I never knew oil caps wore out. Or do they? Am I just seeing some kind of difference in aftermarket parts? If not, how the heck did that rubber shrink that much? Seems like being oil soaked for all these years, it would expand, if anything. Just something I was curious about I guess.

[VileZambonie]

It's not just oil it's heat