I have lived in the Chicago area, but really never used any indies there as I commuted to Wisconsin often and had my car serviced there.
What I would do is to visit the "good MB shops" section of this forum, go under Illinois, and read some posts about Chicagoland shops. There are some shops very highly recommended there, and NOT highly recommended as well - a great resource to start off with.
Then, call the shop and talk to them about your specific issue. Remember to tell them that you found them here - they enjoy being praised, and I'm sure will look kindly upon you for that.
Best of luck!
Michael