I bought a 4200 from ADG a few years ago, cost me around £26k, I didn't get it inspected (Foolish me) it turned out to have been in an accident. Most of the front of it had been replaced. When I went back to ADG they denied all knowledge and were of no help at all, they reluctantly offered to buy it back for about £18k. I ended up selling it for £19k. An expensive lesson.
I would go very very carefully if you go the ADG route.