Well, you seem to be somewhat lucky in this instance, since your biggest problem is the ground down at the bottom. The part above it where the join would be is easily covered up by black or white redraws.
If you're not up to full pattern redraws (probably a good idea, since this looks like it's from a tank volume), I'd suggest trying what you did, but on a slightly smaller scale. In this case, do a copy/paste of the section on the left-hand side immediately to the left of the join. Match it up so that you have the lines all meeting up with each other and you more or less have them mirrored. Then I'd suggest taking a mild eraser to it. Turn down the opacity a bit and go along the edges of the pasted section. That way it doesn't stand out as being exactly the same. If you need to add in some black lines, go with the line tool at 1px, or 2px for slightly thicker lines, if you need to redraw some.
If you have a copy of the raw, I can tool around with it and see if I can come up with. I dunno what's covered up in the bottom right of the page, so you may have done more work than you needed to.