ThinkPads of that era used some kind of rubbery coating material, that over the time absorbed something from the environment that caused it to became this weird goo. I would not be that surprised that this weird icky goo also emits some kind of vapors that some people find repulsive. I would recommend just washing that off with 1:1 mix of acetone and isopropyl alcohol (but well, if you find the smell coming from the goo repulsive, get an FFP3 mask when you do that, as the vapors coming from that mixture are in completely different ball park)