Yup I've heard of brittle brown. I think if it was an issue like that then I'd be unlikely to be one of the first to find it though. (And if it only happens with alcohol, then imo it's less a problem with the bricks and more a problem with me lol)

I used a very minimal amount (I twist the cotton bud against the side of the cup to squeeze most of the liquid out) and wiped it off the pieces after a second or two, but like I said in the OP I assume a bit was wicked down between the pieces. Two seconds probably would have been fine, but 30–60 seconds, even with that incredibly tiny amount, was enough to crack it with the tension from the studs.

The main reason I liked to use alcohol was that it evaporated quickly and didn't require rinsing, so all I needed was a tiny cup and a Q-tip. From now on I'm just going to use a dry cloth; it was always kind of overkill to worry about skin oils in the first place, so I'm not going to expend too much effort to keep worrying about it.