I don't even know... it could have been like this for ages. Since I do my own repairs and I haven't been down here before, I'd say it can't have been touched in 3 to 4 years at least!
I was getting frustrated and just started removing stuff to get a look at the wiring harness. I had found some mouse droppings (on the battery and on some other things) ... so I was afraid I'd be finding mouse chew damage ... but luckily so far I've found none.
I would go even one step further, I would definitely clean and tighten that nut, but I also like adding an additional ground path. Not really needed, has minimal benefits other than its not hard to do and it adds redundancy.