On my SL website (link below), it says:
230 SL's: of 19,741 total, 4,200 went to the US.
250 SL's: of 5,196 total, 1,761 to the US.
280SL: of 23,885 there were 12,927 to the US.
The percentage to the US increased as time went on.
I'm embarassed to say that I don't remember the source of these figures.
Richard M
www.panix.com/~rmadison/mercedes.shtml