Technical Jim's helpful shop tip.

Welcome back, OP, and this is still a good tip. I had similar issues, some of my paint cans were getting a little fuzzy looking and one of my steel shelves looked rougher than the others. Same culprit, a sealed plastic jug of muriatic acid that I got with a whole batch of auto body materials at an auction.

I gave the acid to some guys I knew who are stone/brick masons, they use it all the time. Apparently you can also make it inert with something (baking soda maybe?) and then it's safe to dump out but I didn't want to do that.

 

I had a bottle of muriatic acid sitting next to my toolbox for maybe a week. It ended up having rust blisters on that side.
Old car batteries can be just as bad sometimes especially if they’re in a warm spot or the sun is shining on it.

 

Well Damn, and I thought it was just mouse pee causing the metall cabinet where my wife keeps her pool supplies to rust out.
For years my buddy kept all of his paint including fizz cans and thinner stored in an old long dead fridge outside of his garage that had a hasp and padlock on it. Mostly for fire safety though. One of those could serve as a no cost storage stuck out in a shed away from your garage or regular storage for such chemicals until the chemicals eat it but it would be a sacraficial piece.

 

I'd noticed some similar issues with two or three gallons of "closed" muratic acid containers next to my work area. Last fall I moved I moved it outside...although..come to think of it, they are next to the metal garage doors, maybe I'd better move them again.
Concerning MEK....back in the late sixties I worked aerospace in New Mexico and we used MEK to clean up our test fixtures (we were testing potential flammable materials that went in the spacecraft--a lot of them burned), I was young and pretty tough back then, I find myself using more rubber gloves now

 

A few years back, when everyone who decided they wanted to a Billy Bob Badass Biker started buying Harleys, my son-in-law bought a bright, shiny new Road King with every piece of chrome he could get on it. In the 3 years he had it, he put 2700 miles on it. The rest of the time it sat in his un-airconditioned closed up garage in central Texas right next to the pool chemicals. Last time I saw it, all the chrome was peeling off or pitted and the aluminum was pitted, as well. Surprisingly, the paint held up well.

 

A friend of mine had a jug of muriatic acid under his kitchen sink and it corroded the braided supply lines to the faucet. It caused a flood in his house while he and his wife were away. Luckily, they were able to dry out and save his hardwood floors.

Gary

 

It (HCl, aka Hydrochloric acid) sure is nasty stuff. Caustic liquids were mentioned earlier, but keep in mind that caustic is actually alkali, not acid.
As for the danger of inhaling very small amounts of HCl vapours, it's probably not too dangerous considering our stomachs are full of the acid, it is used to digest food.
But it explains why "acid reflux" can be a very unpleasant ailment.

Another thing to keep in mind is that plastic containers can become brittle over many years and crack or even break up. If you discover a long lost jug of acid, bring a small pail or similar to it, and carefully put it in there just to be safe.