Ask Smithy Xtra Surface rust on Navara

I had to send my 2007 D40 Navara back to dealer to cut off surface rust 10 days after I bought it. The dealer made me pay, as he believed that grinding or welding had occurred close to the vehicle. Difficult to believe, but as I left vehicle in a truck yard daily for 12 hours it was possible. I had two specialists cut and touch-up paint work in the following two years as rust on the bonnet, roof, around the front windscreen seals and on the level areas of front mudguards after each rainy season. A panel-beater said it was cinder damage from transport by train, so I submitted an insurance claim and the insurance assessor also believed it was damage caused while being transported and knocked the claim back. Co-incidentally the assessor was an ex-Nissan Service Manager. I went back to the Nissan dealer, but my claim for the repairs was rejected and I was told damage was caused after delivery to me. Any idea where I go now to solve?