Thanks a bunch for your insight. It's always intriguing to read.
Yes, I have seen a drain plug left untightened by one of the most impressive truck mechanics I ever knew. He was a salaried tech in a large major brand truck shop. I had just gotten out of the army and was a service writer there part of the time I was in college. This was thirty years ago and I don't remember how much the repair cost was, but it was probably a few weeks pay or more. He really felt terrible about it, but things happen. I saw him really working even extra hard after that in an effort to make it up to the shop.
He developed a habit from the experience that I learned from him and still use today. After that he never (and I have never) threaded in a drain plug without the wrench for it in his other hand. This way if he was called away for any reason, he could tighten it before leaving.
Even as absent minded as I am, this has worked for me for thirty years so far. Of course, I don't work in a shop for a living, so I have had relatively few chances to make this mistake.
The pro techs are human, the best of them will make mistakes.
Thanks again for your insight,
Gray Market Survivor,
From your description, I expect that if the truth could be known, the first tech that replaced the upper control arm lightly snugged the bolt on the sway bar and it coincidentally started rattling and them came out after the lower control arm job.
I hope I don't sound condescending or anything when I say that you should have investigated the noise immediately after hearing it. We all learn this kind of thing sooner or later, and in my case I probably have even been guilty of such a thing even after learning it earlier.
BTW, I'm quite envious of your 5 speed 300D. The ones sent to the US gave us the extra cylinder but made us take the automatic transmission which robbed the extra torque from us.
Best of luck,