I still have a ton of carbon, and always check them before I use them.  The military versions with the green body seem to do better than others on longevity.  I have tried on an experimental basis, to heat NOS out of tolerance resistors in a 200 deg. over to dry them out, and they do return to their marked value.  But after a period of time they again take in moisture and go out of tolerance.  The body must have micro size cracks or maybe where the lead enters, leaks air in.  To be honest, I am still not sure about the modern resistors and their make up, metal film, carbon film, etc.  Other than not using a wire wound in an inductive circuit, I do not know or believe some of the claims, especially by audiophiles,  about what resistor to use due to noise/   Plus, in our RX's and TX's, whether composition makes a difference, or to worry about noise in audio bandwidth where our concern is in the voice intelligibility spectrum of 300 to 3000HZ..  I will say one thing about new resistors, the banding on some, especially the dark blue  one is impossible to decode, the blue body obscures the real color, and now I have to double check what I think it is with an ohm meter.  Also, if I do not keep my orders in the bag they came in or in marked storage, the modern 2 watt resistor is the size of a 1/2 watt  carbon, while not an issue due to the wattage in a circuit less than 2 watts, don't like to waste a 2 watter where a 1/2 watt is all I need.

Charlie W4MEC in NC