I have a 17Reg T6 and kept noticing rust particles on the step as you open the sliding door. I confirmed it was not from the sill or step. I had suggestion it could be rusty swarf from the conversion, but today after closer inspection (on my back on the drive) I peeled the rubber seal around the door and found rust appearing to bubble behind the seal. I've taken it to VW Newbury bodyshop who looked at it favourably and have taken details and pictures and will be sent for a yes or no.
Hard to take a picture upside down of the inside of the door, but thats the best i could do.
Hard to take a picture upside down of the inside of the door, but thats the best i could do.