When I joined them to cover my car's gearbox, they did not explain that some parts within the gearbox are not covered

When I joined them to cover my car's gearbox, they did not explain that some parts within the gearbox are not covered. Now that my gearbox needs fixing, I need to pay R73000,00 because, they argue, I should provide them with service history from a reputable company, which they did not mention when I joined them.