I am not sure it should break in. The system is self adjusting so they should always be adjusted correctly. Have you pulled the valve cover and had a look to make sure everything looks okay and the cam is getting oiled. It is messy but well worth it to check.

I assume you got the right came for your specific engine, MB cams vary based on the engine designation. I am sure you did but just checking.
m

__________________
Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)