This is the latest information that I have been advised on this cracking problem from the USA, but the comment has not been confirmed by anyone outside the USA as yet:
"The subframe cracking problem problem existed on all SL's delivered worldwide, mainly 450's because of the weight, not 560's as they use a different suspension.
It was only in the USA that there was an actual "recall", forced by the NHTSA and the sue happy US system.
In all other countries the customers received a letter from their dealer to bring the car in for inspection and/or repair. The order for this letter originated from MB Stuttgart, as is the normal system in such cases."