Some background: I was working on my friend's car, a 2012 Chevy Sonic he'd bought new. He had previously had both front stabilizer bar end links replaced, one under warranty and the other by Midas a year ago. (These are plastic shafts with a ball-and-socket at each end; the socket wears, and they start knocking over bumps.) When he was at Midas a few weeks ago having his tires swapped over (winters to all-seasons), they told him his struts needed to be replaced. (The front end was making various evil noises - knocking and thunking and rattling harshly.) He brought it over for a 2nd opinion, and the struts looked OK to me - but they did have over 100K km on them, and he wanted to proceed. We did the driver's-side strut first, and found that the stabilizer bar end-link previously replaced under warranty was shot - lots of play in the lower ball-and-socket. OK, there's some of the noise. These are always a challenge here in the semi rust belt. (Due to our extreme cold, it's not as bad here as southern Ontario or Quebec, but stuff does rust. There's not too much oxidation happening at -35 C, but this past winter was terrible with a number of freeze-thaw cycles in March. I was riding my bike home during a thaw, and tasted salty brine every puddle I went through, for example. Imagine that stuff getting sprayed all over your undercarriage.) Any of the FWD Asian cars I've worked on use a style of end link whereby one is supposed to use an Allen key or a Torx bit in the end of the threaded shaft to stop the ball from turning in the socket while one removes the nut from the threaded shaft. Terrible design for this climate, as one is limited to using a wrench rather than a socket, and there's no way a small Allen key or Torx has enough strength to hold the shaft while one is trying to turn off a rusted-on nut. I wish they would install these with anti-seize compound!!! Anyway, we disconnected the top of the end link from the strut, which was easy, but when we had to disconnect the bottom from the stabilizer bar, it was a nightmare. I finally had to grind it off. Very challenging, as there was very little room to work. GRRRR! The new strut and end link on the driver's side got rid of the distinctive knocking noise over bumps, but not the very harsh rattling noise. We moved over to the other (passenger) side, and had a heck of a time getting the top nut off, but finally got it after about an hour, with liberal application of penetrating oil, and going back and forth with a wrench while trying to keep the ball from turning. This on a part that had been installed by Midas only a year or so ago. Wow, rust never sleeps. At that point I had to pack up for the day. My wife and I went away for a few days cycling, but I gave my friend my rattle can of PB Blaster and asked him to soak the bottom nut and threaded rod a few times while we were away. This was more or less an act of pure optimism on my part - on the other side the bottom nut was much harder to remove than the top. How much worse would this side be, with the top nut on this side so much more difficult than the top nut on the other side??? He brought the car over yesterday, and we found the source of the harsh rattling sound - the bottom nut on the passenger-side end link had backed off several turns, and the threaded shaft was moving in the the stabilizer bar hole. We presume that the nut had worked loose sometime after Midas had installed it. It's interesting they didn't find it when they diagnosed the struts as being bad. We also found that the link had been installed upside-down - the plastic body of the link is marked 'STRUT' or 'STAB BAR' at each end. (You can barely see these embossed markings in two of the photos.) The link looks the same either way to me, but they had installed the stabilizer bar end on the strut, and vice versa. Perhaps that led to the nut working loose. Just a guess. But here was the surprise - the bottom nut came off with ease. I know it's not a controlled experiment, but it sure seemed that waiting for a week, and applying penetrating oil regularly over that week, made a huge difference. Facing this sort of situation in the future, I will definitely try to make time to pre-soak the parts to be removed with lots of penetrating oil for a few days in advance. We installed the new links properly, and used plenty of anti-seize on both sides. The car drives quietly now. We saved both struts, as I really don't think there was much wrong with them.