Could be bad seals in the ram, bad valves in the gear box, leaking or a clogged hose. If you take it to a Corvette specialty garage they can probably fix it as the same ram assist power steering system was used on Corvettes from 1965 through 1982. Corvette restoration houses will have replacement parts as well as quick ratio steering upgrades. Because it involves a Corvette it will be expensive as Corvette parts cost more than Impala parts the same way Cadillac parts cost more than Impala parts. They think because you bought an expensive Impala (corvette or Cadillac) you have more money than sense.