I'll dig some photos out of when I did mine on my old 2cv. If the sweeps are fucked then there's a good chance the rear light panel underneath is on it's way too, and if so it's best to change this at the same time. Really easy bit to change, but don't be tempted to do what some so called specialists do and hide the seam with wag, Citroën never did it and it screams out 'bodge' even if there's sound metal underneath. When I did mine I welded the new panel on flush (not overlapped as paul suggests) with a big old copper block behind it. I then sanded off the weld until it was just slightly proud and finally finished it off with a sanding block and progressivley finer grit paper. On the inside the weld was behind the two lugs on the back panel so I didn't (couldn't) finish that to a similar standard. Basically I made sure it was straight with a strongback while I tacked it in and you can hold a level on it now it's painted and it's perfect. Bodyshop didn't use any filler and the joint is invisible. (unfortunately the pricks didn't spend very long prepping and painting it, and the back panels crying streaks of rust, but that weren't down to me, they won't be getting my business again though!)
Pics when my computers back from the shop.
