2012 GLK350 Parking Brakes
 

Parking brakes wont return after release. The foot mechanism needs a little help to return. I lubricated the cable in infront but could not lubricate the mechanism as it had a cover and i cant figure out how to remove it. I havent looked in the backside(rear wheel). Anyone encounter this with the GLK?

Parking Brake release on GLK 350
 

I have a similar problem on my 2014. The Parking Brake won't release without some coaxing. I found several complaints about this on MB World and the control part is available from several parts houses. So it appears that this is a common problem. Mine is still under the CPO Warranty so I took it in today for repair. When I get it back I'll post what they did to fix it. The P/N for 2013-2015 is Parking Brake Control - Mercedes-Benz (204-420-15-84) and the list price is 187. I found it for 158 from a dealer.

Parking brake fix
 

I got the car back today and the Parking Brake works properly now. They replaced the Parking Brake Pedal Assy. P/N 204-420-15-84. I can't provide any cost info as it was under Warranty for us and 0 cost. :D

happy wheels
 

I have not had a problem you shared, I think you should change the brake to be safer.
Temple run