I cloned the left barrel, actually selected a section of it and duplicated it twice. I then shuffled the three layers around, flipped one or two horizontally and also skewed them to better fit on top of the right barrel. I then used the Clone Stamp to make a transition between the sections.
The middle part of the right barrel is mostly painted, I did, however, also clone some from the left one.
There is a lot of trial and error involved and I wound up using about 20 layers...
Juergen