Thank you, Noodles.
I was also not impressed with the one technician I spoke with at the dealer, when I was doing the pre-purchase inspection with the car up on his lift. He was a shady character, making stuff up as he went along to try to just get me to buy the car.
Just one example, when I pointed out that the rear left muffler was leaking at the flare connection, he said, "oh, Mercedes makes those joints leak on purpose so that water doesn't build up in the exhaust system and make it rust out."
So, I am not surprised that his (or another technician's) work was subpar.
The salesmen were nice and gave me the car for a fair price. That's about it.
I live by the adage that "when you want something done right, do it yourself," much to the chagrin of my dear wife, because this means I spend quite a bit of time under our cars
I will do this repair and report back.