sentences:  Unfortunately the early engines suffered from heavy wear of the rotor tip seals in the innovative Wankel engine, causing severe financial losses for NSU.37,204 Ro 80s were built by the time production finally ceased in 1977, but by that time the company had long been part of Audi, a Volkswagen subsidiary.The K70 was originally created by Luthe as the NSU K70, to fill the gap between the Prinz and the Ro 80, but came to the market in 1971 as a Volkswagen K70, after considerable delays, partly due to the Volkswagen acquisition of NSU, and with modifications to Luthe's original design.