As a German living in Germany, I join in the question “Where did they all go?”. Even in Germany you won`t find many Opel Kadetts “A-D”, the D-Kadett was built until 1984, being regularly driven anymore. Even at classic car shows that my wife and me attend with our cars you are sure to see at least about 30 vintage Porsche 911 or Mercedes SL for every Opel Kadett oder rear-wheel-drive (built until 1980) Ford Escort.
Opel campaigned the car extensively in motorsport too. The rally version was uncompetitive, but Opel eagerly waded into the 160mph traffic jam that was the International Touring Car Championship. The ITCC was created from the German DTM series, in which Opel had struggled. A rule change allowed Opel to use a new 480bhp V6 derived from the road car. The resultant four-wheel-drive monster carried Manuel Reuter to the 1996 ITCC driver's crown and Opel won the manufacturers' gong, beating Alfa Romeo and Mercedes-Benz. It was the Calibra's finest hour.
It had some crazy mechanical issues. At one point it stumbled and stalled because the carburetor had come loose from the intake manifold and I had to tighten it back down! Another time, my brother was driving it and the brakes failed. Somehow the end of the brake shoe that meets the brake cylinder piston had become worn on one side, causing the piston to slip off the end of the shoe when the brakes were applied, losing braking and squirting fluid all over.