Hi, I'm going through the same thing. I have an X55 SS vert from AZ. Extremely clean, but that Arizona desert dirt acts like an undercoating too. When I bought it I had to steam/pressure wash and it came out damn near perfect, one thing though, it took alot of the black paint with it. Any suggestions on repainting the undercarriage and engine bay so I don"t ruin the original look? This too is a #s matching original car. It does have 1 recent repaint in #40 original butternut yellow. Thanks