SLK230 sticky lock problem
 

Hi, I have a 2003 SLK230 with 64k miles and am struggling with locking system. I've replaced the key and tumbler but the lock is still sticky, sometimes doesn't turn at all. Unfortunately I've heard different opinions from 2 different dealerships and not sure what to do. One suggested replacing the steering lock mechanism which is a costly fix and has no guarantee. Any thoughts? Thanks for your help!