I just picked up another N64 and noticed a lot of rust/scratches/corrosion to the reflective outside portion of the cartridge slot, and pretty much all of the metallic shell on the underside of the console, including the underside extension port, so something must have been spilled in it or it's spent some time in a garage or attic. Games play okay but I don't really trust it, feels like I'm sticking my carts into something you'd pull out of a car with 350k miles on the clock. The metal components on my other N64 are gleaming in comparison. Is this just standard condition for an N64 these days or has something bad happened to this machine? Any danger to the carts, or is there anything I can replace or clean the corroded components?

I would guess if it's not damaging the pins of the cartridge it should be ok. I've seen a lot of them in the same condition you are describing.

I kinda understand the car analogy, but I wouldn't worry too much about it if the games play fine. It's probably best to get some rust remover at Walmart or something and clean it up with q-tips just in case or for just a piece of mind. 

Also you could try and use a old credit or debit card and wrap a thin 800 to 1200 grit (Don't go any lower than 800) and some alcohol or electronic cleaner to clean out the pin connector in case there's any gunk in there. I usually use just a credit card in case I find something like dog hair in them.

Good luck!

Thanks guys. The pin connectors seems fine, it's the metal shell that's heavily marked. But I'm sure a lot of NES and SNES machines look like this too by now.

My vote is that it was stored in a moist basement. If it works, ride it out, N64's are crazy reliable. I'd clean the jumper/cart pins and give it hell personally.

All this talk of the damage to your N64 and no pics? Meh

I'm also in to see this bad boy!
 

Look something like this?

https://imgur.com/a/0MsxUjk...

I bought this system at a garage sale. It was dirty and rusty, but played and operated perfect.

Ha, nice. Mine was cleaned at least so it doesn't look that bad. Mine also plays fine, and someone who knows better than me took a look and said I was overreacting, so I'm not going to disappoint you all with the pictures. I'm just going to use the console until something goes wrong. It has a great video output mod so I'll live with it.