it's possible you got some rubber from before they started using an ozone stabilizing formula, tho I can't imagine why the cats whiskers would deteriorate .... you could also have stored it poorly, a stable cool temp and dark is best, and left in the plastic bags .... rubber from Steele is excellent quality [better than OEM], they should have most of the 60-66 stuff, if that's what you have
the hornets nest is folks complaining about Chinese parts

Bill