Battery went dead in my car overnight, why?

I have an OLD car: An 89 Oldsmobile, Delta 88. It's falling apart in a number of ways, but all of its problems are mostly cosmetic and "comfort" related. For the most part, it runs great. Engine is in very good shape with 120k miles. Breaks are good, transmission is good. However, I have... show more I have an OLD car: An 89 Oldsmobile, Delta 88.

It's falling apart in a number of ways, but all of its problems are mostly cosmetic and "comfort" related.

For the most part, it runs great. Engine is in very good shape with 120k miles. Breaks are good, transmission is good.

However, I have noticed lately that the floor on the driver's side is /very/ wet. I haven't noticed any leaks, but it's remained wet for weeks now (I keep it outside and I live in Seattle).

I've been mostly just ignoring this (and it may or may not be related).

This morning, when I tried to start my car: nothing. Absolutely nothing. No lights, no horn, even door locks don't respond. It's totally 100% dead.

I'm wondering if there is a leak which somehow caused a short and drained the battery? Total guess though, and I am no car expert.

What else might cause this? How can I troubleshoot it?
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