Hey guys, I wanted to update you as well as for archive reasons.

So I had my CL500 flatbeded to my mechanic. I explained the problem I was having along with the probable diagnosis. Sure enough it was the parking brake mechanism as stated above by Manny (Thanks).
Part Number-140.420.09.20 . The parking brake springs were broken by the length of the lug-locks on the rear wheels. So they replaced the entire mechanism including the brake shoes and springs.

So the lug-locks were apparently the correct lug lengths for the OEM wheels from MB but unfortunately they were incorrect for the after market 20" wheels I have on the car. An expensive mistake but at the end of the day just a mistake.

Thanks to everybody for their help.