We don't ship them in diesel. We store them that way.
The hold down bolts have as much to do with how well the injectors seal as anything. The bottom seal on the injector is brass; not copper. The brass seal does not deform like the previous 2-stage injector copper crush washers. In my opinion, unless the brass seal is damaged, they don't need replaced. The cylinder head seal area should be clean and flat. The red/orange bottom seal needs to be in good shape. If you get a lot of black soot on your fuel filter or blackened fuel, that bottom seal is usually the problem along with the correctly tightened injector hold down bolt.
The hold down bolt is an aggravation. If you reuse a OEM bolt, you risk breaking it off flush with the head. If you use an aftermarket bolt, which are non-stretch, they end up pulling the threads out. We feel it's an imperative to use the OEM bolts. There are many with experience that agree with us that 78 INCH lbs, + 1/2 turn is appropriate. By the book, the bolt should be tightened to the preload + 3/4 turn, but that makes me pucker. From my own experience in my own vehicle, one-by-one the injectors pulled the threads out and the injectors popped loose. I installed double-depth recoil kits in the cylinder head to repair them. With that install, we think you can safely load 3/4 turn. I might also mention, when testing injectors, we install with preload and 1/4 turn. The bolt will hold the injector well enough to test for balance, yet the bolt has not been stretched. It can be reinstalled to a finish torque and still be good.
Otherwise, what we have found is that the seals generally aren't damaged except for the bottom seal, which either melts or leaves a scab in the hole. The two black seals are often in good shape, however, we find the injector bore will often have a burr near each of the top two seals, which can ruin the seals on reinstall.
The hold down bolt and block tend to push the injector so it leans against the opposite side of the injector bore from the bolt hole. The steel of the injector will vibrate against the bore causing an aluminum burr to rise up. The burr is sharp enough to cut the two top black seals on reinstall. We polish that burr out with a small 240 grit flapper wheel on a die grinder. You can use fine emery cloth. If the burr is not removed and any of the black seals are cut, all the pressure from the tandem pump is lost to the return fuel galley. You will suffer fuel starvation under hard acceleration. A cut top seal will lose fuel into the engine oil, although that is not as common an issue.