Mercedes B200 W246 Steering rack Knock

[sijames04]

I have a 2012 Mercedes B200 (w246) which has developed a knock in the steering rack when you wiggle the steering wheel. After doing some research is looks like the steering rack thrust bush/bearing is worn and needs replacing. I've seen a lot of bmw's and Mercedes sprinter vans with the same knock and the part is readily available and seems to fix the issue. However when contacting a Mercedes Parts specialist to see if they stock the part, I was told you can't purchase the part separately and a whole steering rack would need to be purchased which seems insane given a new steering rack is at least £500 and the part I need is only around £30. Has anyone had any experience with the issue and could possibly point me in the direction of where I could get the part as I can only find it for a C or E class. I've attached a picture of what it looks like