I have not gone there myself yet, but a co-worker who is both a car and Harley guy says good things about Fabson Engineering AG, W63 N133 Washington Ave., Cedarburg, 262-376-0427
I've only gone here twice: Presitige Auto Service 2035 W Bender Rd, Milwaukee, WI 53209 414-351-9242 but they've been in business for years and seem to do good work.
You can also check the Milwaukee chapter of PCA for shops here:
Porsche Club of America - Milwaukee Region: Resources
You driving in this weather?
DBear