Air kills cartridges?

Rubber suspension components deteriorate, primarily because ozone attacks rubber. This is oxidative deterioration. Rubber also deteriorates beause of crystallization, causing it to lose flexibility. Cold storage impedes oxidative deterioration but accelerates crystallization. This low temp crystallization can generally be reversed by heating though.

Dopgue is right, the deterioration issue seems to be exaggerated often. I too have cartridges 30 years old that sound fine still. Another good product is "Rubber Renue" by M.G. Chemicals (mgchemicals.com.) I've never tried it on my cartridge suspension, but it works great on grommets, gaskets, belts, etc.