Problem Solved.

I used to work at a car wash that also did detailing.  We had a customer complain about a spot on a car that wasn't there when they put it through the wash.  My manager dismissed it and didn't take responsibility for the spot which seemed alright at the time because we had no way of knowing where the spot really came from, but once I started to notice the same mark appearing on other cars I knew it wasn't a coincidence.  

I didn't have much to go on, but I was able to determine that it was only happening to cars that were getting the "super" wash with all of the products we used offered so I figured that it was one of the products not used in the “basic” washes.  Also, by the fact that it was showing up on cars at all meant that it had to be later in the wash otherwise it would have been washed off rather than sealed on.  Using this information as well as noticing that the spots were generally in the same spot, I began to look through the tunnel to try to find where the issue was coming from.

  I determined a point in the process where it made sense that the spot could be coming from, and then searched the area to find that one of the pipes seemed to be acting differently from the others.  I followed the piping back into the chemical room and down to the barrels of chemicals.  I confirmed that I had found the right barrel by the color of spots left on the cars, and was able to determine that the root issue was a faulty valve that controlled the chemical volume.  I was able to inform my boss and stop any other cars from being damaged.

I didn't know it at the time, but looking back it was surprising to notice that I had used several problem solving tools at least to some small degree. 

SH