When To Retrofit
WARNING: This page does not describe the selected car, but rather 41 other vehicles, including the 2003 BMW M5, 2003 BMW M3, 2003 BMW 540i, 2003 BMW 530i, and 2003 BMW 525i. However, it is still accessible from the selected car via links, so may be relevant.
As long as R-12 is available, it should be used to service a vehicle with an R-12 system. When R-12 supplies are unavailable, the customers may be willing to pay for a retrofit.