8k is enough for sludge to form. Especially if that’s been consistent. I don’t think your neighbor would go out and be able to add anything to sludge it over night, let alone having access to what I would assume is a locked car. So I’m going to say no foul play, just a lack of a better maintenance schedule.

Nope. No can fix that. It’s probably worse under the car. Invest that money in a different car.