I was washing my wagon yesterday, and noticed that the gap between the hatch and rear fenders was not even on both sides of the vehicle. See the photos below:

https://imgur.com/a/UrObBdz

Is something to be concerned about? Or can I adjust this? Regarding the driver's side bumper, it is sagging because the mounts are rusting out, but I'm welding in new ones this month.

 

Nothing to be concerned about unless it is related to rot. Could be just an alignment issue or it could be the car was in a previous rear end collision and cannot be aligned perfectly.

 

No accidents on record, and while the car has rust, it is all superficial and surface. Is there any way to adjust the alignment for this?

 

I would guess at some point in its life, it took a superficial parking lot bump in the rear; and those sort of things rarely appear on vehicle history reports.

See if you can cheat the gap by splitting the difference by moving the hatch gate (you should have a little side to side play when you undo the upper mounting bolts. If that doesnt help, I would move onto the passenger side rear corner, where you have little or no gap between the body lense and hatch gate lense. Try taking the the body lense off, along with the filler piece below the light; and see if you can put any outward pressure on metal. If it feels like there's any give, then take a rubber mallet and very carefully tap the body outward. Dont go too crazy, as that's all very thin metal; and check where you're at every so often by throwing the lense and filler back in, and close the trunk. Keep doing that until you end up with a gap you can live with.