Complex sentence: The Electro 35 GS and GT were introduced in 1970 (and all later Electro 35's) have all internal electrical contacts gold plated to prevent oxidation from impeding the flow of electricity around the circuits.
Split into simpler sentences: The Electro 35 GS and GT were introduced in 1970. They (and all later Electro 35's) have all internal electrical contacts gold plated to prevent oxidation from impeding the flow of electricity around the circuits.