An elastomer composition includes a polymer system made up of a majority of HNBR polymer and an optional polymer additive such as carboxylated nitrile, ethylene-propylene-diene rubber, isoprene rubber, chloroprene rubber, acrylonitrile-butadiene rubber, butyl rubber, isoprene rubber, natural rubber and hydrogenated carboxylated butadiene acrylonitrile terpolymer, and combinations thereof. The polymer system totals 100 parts by weight. A cure system for the elastomer composition includes 1.5 to 30 parts by weight of zinc, magnesium or calcium oxide, 15 to 50 parts by weight of an .alpha.,.beta.-ethylenically unsaturated carboxylic acid and an organoperoxide. Under vulcanization conditions, the elastomer composition cures through the in situ formation of a metal carboxylate. A degradation inhibitor for an elastomer composition that includes an amine and an imidazole along with an optional polymerized quinoline is noted to be particularly effective.