My 2003 Cobra had bad vibration in the mirror like you describe. Had to have the driveshaft replaced, that cleared it up. Was a common problem with 2003 Cobras.
We have that in our Hyundai Genesis Sedan and I use it all the time. Good way to get a quick read on your speed without having to squint to see the smaller numbers on the speedo. Getting old and needing reading glasses is a bitch.
summer tires in cold weather create traction issues. Not only for accelerating, which can get you sidewise, but also think about the traction issues on braking. Not being able to stop quickly or slowdown when someone pulls out in front of you is an issue. Get all seasons or winter tires if...
Post the shop name here, and on every other enthusiast website you can find, do the Yelp thing and other review sites, see if you can get a refund or partial refund from the owner, and then let it drop. Life is too short. A bummer for sure, but unless they damaged anything on the car, you are...
get a good set of winter tires on an extra set of rims, and put three bags of water softener salt in the trunk for the winter. You'll be fine. I drove my 2003 Cobra year round for eight years in Waukesha County following that recipe, and it was still in great shape when I sold it.
you should really drive a GT500 and see if you like the way the solid rear axle handles through any curves that aren't new pavement smooth. IRS is a big improvement.
With good snow tires you will have no problem in Chicago other than on the very worst of days, when you should stay home anyways. I live just west of Milwaukee and have driven the following Mustangs without issues year round, including in the winter in snow storms:
1999 Mustang GT Convertible...