I bought a 171 van about a month ago from a simi registered dealer which still has manufacturers warranty. After purchase I noticed the parking assist system was not working. So I took it to my local vw dealership who, after,assessing the fault, confirmed it was covered under warranty. Dropped the van in today to get the work done and they've contacted me to say they found previous wgork done that is not vw so now not covered. 600 euro. I bought car with full vw service history and warranty. Contacted dealer I bought it off as I think they should stand over it. Also, I never would have agreed to the work if it wasn't covered and took the risk of having to pay for initial assessment at vw. What options do I have here?