Just no. Pull out any rare isa cards and incinerate the monstrosity.

Yummy! 🤣

I got a bunch of PCs from a business ~7 years ago, and they had been in storage for a long time. The oldest one was a, I believe, a Compaq Presario tower. One of the large funny\bulbous-fronted ones from the Socket 7 Pentium era. Anyway... it was clearly not in the best condition on the outside, but when I opened it up I discovered that it had apparently been used as a mouse apartment building for a very long time. There were "mouse drippings" stains all down the ribbon cables, as if they turned them into their own personal sewer system. Huge wads of fiberglass insulation were packed into different places in the system too. It was so nasty. Since it was actually a pretty high end PC from the time it had some decent components so I salvaged a few and just junked the rest. It wasn't worth the time and the health hazard trying to clean it up at the time.

I'll disassemble and clean thoroughly every case and build I buy. I've never found anything worse there than dust, hair or cobwebs and mummified insects, but on one SB32, spider acid??? tickled the connection between the transistor and the capacitor.
I know it sounds weird, but the card was a long way from a CMOS battery that could leak an electrolyte, it was on the opposite side of the board and only this small area as a drop, so I can only think of spider acid because there were remnants of limbs from some insects.

Yeh I always strip down and clean a computer. It doesn't have to be spotless like some people seem to aim for but it's a god way to get to know what your working with better as well.
I've had some computers from industrial businesses that are absolutely filthy but luckily its always just the typical dust, insects, etc. never anything that I would be scared to touch.