general problems of the 1999 Volkswagen Cabrio

Convertible top accumulating some kind of black substance that hardens and cannot be removed. At the three year mark, the car just began to deteriorate very quickly. Timing belt, convertible stopped working, abs brakes kick in when not supposed to, exhaust system had to be replaced at 40k miles. Key lock button fell out, cannot get it to stay in. Seat belt assembly fell apart. Interior door handles not made well, loosened and feel as if they may fall off. Cd changer has never worked properly.