2012 Leaf clunk in rear suspension on bumps.

Hope this helps someone else.
Several weeks ago I bought a 2012 Leaf SV that had a warranty battery replacement, so it has as-new range.
When I started driving the car I noticed that on each larger bump I heard a clunk coming from the left rear wheel direction.
I crawled under the car and to my horror, the two new brackets on the replacement battery were fastened to the battery
but not to the car. The 17mm bolts were hand-turned 2 turns in their threads and I needed to tighten them another 5 turns or so
before the two new brackets were actually held to the car above the rear axle.
I thought I had fixed the clunking, but upon driving the car I noticed it was still there.
I looked under the car once more but there is not much that can be wrong besides the strut and it looked fine.
The clunking continued and I even jacked up the car to pull and shake on the rear left wheel, but everything felt tight.
I got a good bright LED light and crawled one more time under the car and then I saw it:
The lower bolt of the left wheel strut had a brown dusting on it as if it was rusting while the right side bolt was clean.
What was going on? I had pushed and pulled everything and nothing moved!
So, I decided to try and tighten that bolt.
Unfortunately NISSAN decided to use 18mm bolt head and nut, which is a size that no standard Metric wrench set has,
so I had to revert to using a crescent wrench and my large pliers, but I was able to tighten the bolt half a turn.
Tested the car again - no clunk.
So, if you hear clunking in the suspension then *something* is loose. It might not be a broken strut, especially if you see no leaking.
My strut was perfectly dry and looked perfect and no suspension issues could be noticed during driving other than the sound.
I think I am going to drop by the dealer tomorrow and ask if they remove the rear axle to replace the battery (they should not, but it might be done in order to get at the bolts in the battery brackets which are above the rear axle).
Anyway, just posting as it was driving me nuts so it might help someone who is also pulling their hair out, but not yet desperate enough to go to the dealer. (I avoid dealers like the plague and have in fact never bought a car at the dealer and will only go there for specialty parts or free warranty repairs due to recalls or special service campaigns)

Actually, after considering the rust that I noticed around the bolt head at the bottom of the strut, I am now of the opinion that Nissan forgot to properly tighten this bolt in the factory or the strut was worked on early in the life of the car, because a car in California does not rust a bolt in a few weeks or even months since battery replacement. It has likely been this was ever since early in its life, possibly from factory although that would surprise me. I do not have the service records from before the second owner and she only had the aux and traction batteries replaced.
Anyway, it was barely loose, just so that it could move on a bump and with tightening it half a turn there is complete silence when going over a bump now, just the way I like it.