You need a fully equiped chemical laboratory to evaluate the chemicals in their original state plus and fully equiped physical test laboratory to determine rheometer cure times, viscosity, hardness, tensile, perhaps tear resistance, dynamic modulus, ozone resistance, etc.
At a minimum I would look for changes in rheometer cure times, viscosity, hardness, and tensile properties. Take a look at
in the R.T.Vanderbilt rubber handbook you can see what to check on each raw material, in Rubber plants you check the Mooney Viscocity of the raw rubber and some more like the moisture of every powder, etc