I had the cables replaced on both of my 4021s and the grill replaced on one of them last year. I dealt with DPA in Longmont, CO who sent them to Denmark for the actual repairs. Took about a month from when I sent them out to when I received them back from Longmont. This was with ground shipping both ways. Cost for the 2 cables, grill, check and re-calibration was $438 plus shipping.
Here is the contact info for the folks in Longmont:
Jarrod Renaud
Service Manager
DPA Microphones
1500 Kansas Ave. Suite 3A
Longmont, CO 80501
P: (303) 485-1025
www.dpamicrophones.comserviceusa@dpamicrophones.com