I've been studiying many threads here to determine which shampoo to use and had pretty much settled on P21S BCS for my new black Jetta (PBS is my first choice, but seems too $$$). I just checked the VW manual to see what the mfr recommends and they basically say to use water only. "Use a special car soap only for persistent dirt". Now I'm really confused. Any advice on what to do -- water only or a gentle shampoo? Thanks.