I'm not sure you are interpreting those entries on Etymology.com the right way.
The Latin verb reparare ("to repair"), stem repara-, acquired the adjective reparabilis ("repairable"), regularly formed by the suffix -bilis in classical Latin. This then changed in French, a language which evolved naturally from Latin, into reparable during the 16th century. English borrowed this word again from French.
The past participle of reparare was regularly formed in classical Latin as reparatus ("[having been] repaired"), stem reparat-. In Late Latin, the action noun reparatio ("the repairing") was regularly formed from this by adding the action suffix -io, stem -ion-. The stem of this new action noun was (regularly) reparation-. In the 14th century, this word was borrowed by English (I suspect that it was also borrowed through French, but it doesn't say so).
The etymology of operable and operation is similar. Latin operari, stem opera-, leads to adjective operabilis (it doesn't say whether this word was actually formed in classical Latin, or in later Latin, or only hypothetically in successor languages), borrowed as operable in English ca. 1640.
Past participle stem opera-t-, leads to action noun operatio in Latin, borrowed/changed by French as operacion, borrowed by English from French as operation in the late 14th century.