Like most early D2s mine has a lot of rust in the rear section of the chassis behind the rear axle, and I have cut nearly all of it out and made up the sections to weld in from 2mm steel, it's quiet shocking how much needed to be chopped out (the inner faces of both rails and the most of the lower face and the outside faces by the tow bar mountings).
However I did then start removing the rust from the cross member that sits above the rear axle, and have found even more air where there should be steel, its the area just by the tank mountings, about 1cm high in the rear face, almost the full length has anyone repaired this? and when will the rot removal stop!