I don't think an extra ground cable/bonding strap will harm the car. If anything, you add another low resistance path for the electric systems and it will reduce the electrical noise. Why Mazda didn't install 5 cables or whatever , they installed just one or two? Maybe because in the...
Removing the back seats is super easy. To remove the back seats, the bench, look in front of the seats, left and right, there are two tabs. Flip those to unlock the seat then lift the bench, it should come off. See the video link for more details. Check under the seats, there are some connectors...
On my previous 2020 CX-5 NA I've had the same combination, Pennzoil Ultra Platinum 5W-30 and, most of the time ,93 V-Power Nitro from Shell. But I'd say it was running the same, whether it was Shell Nitro gasoline or H-E-B 93 premium gasoline or Chevron 93 gasoline or whatever. I can't say...
I don't have a local shop and I'd imagine that it would cost more than 600$ to just go to some shop and ask them to make an axle back for my car, I don't know. Paying for one already built seems to me the easiest route.
I would try to drill a small hole on the side, somewhere and dry it through. Then seal the hole.But this is just theory, not sure if the plastic won't crack and then you would have to replace the headlight anyway.