The Manta enters the lake facing away from shore, but is pulled out the other way around.
When Berti drives a race against a VW Golf, both drivers pull the handbrake and press the pedal to burn some rubber. This is not possible, because the Opel Manta is a rear wheel driven model, and the handbrake also brakes the rear wheels.
The Manta from the lake has a front grille with a double air intake, so it was produced before facelifting in 1982 but the Manta used in other scenes has a quadruple air intake, so it's a newer model.
While Berti and Gerd are on their way to the stadium, in the shop-windows you can see the reflections of Berti's Manta sitting on something like a trailer when the camera shows the inside of the car.