Oldsmobile
Oldsmobile's best era was the 1970s and 1980s, with sales being in the all-time high due to positive critics, iconic designs and models, and quality/reliability with the best-selling model being the Oldsmobile Cutlass. This caused it to go into the millions in terms of sales and displacing Pontiac and Plymouth as the third best-selling, just behind the two most popular/known car companies, Chevrolet and Ford. However, this soon became a problem for Oldsmobile, as the production capacity was too high for the Oldsmobile V8 engine. As a result, the engine of Oldsmobile models was replaced by Chevrolet's 350 cubic inch V8 engine, which was discovered by customers years later, which turned into a nightmare for GM. This declined sales, causing GM to create a new 5.7L Diesel V8, which soon turned out to be one of the worst engines in history, causing it to be discontinued in 1985, quickly being replaced by newer, more reliable engines.