While this thread is getting old, I'll add some recent experience. I used JST connectors on my 10 coro mini-trees.
It has been very rainy the last few days (tornados, too, but they haven't been that close), so I looked inside my connectors.
The area around the +12v was slightly discolored. Not damaged or corroded, but all 10 JST connectors showed the exact same discoloration. (galvanic action, I'm certain)
I had not squirted them with CorrosionX.
Now I have. I'll keep an eye on them.
Keep in mind that if you have Pixels attached to a Hub or F16 or whatever, the +12v is hot 24/7 unless you do something about it.