I have never been able to  tell the difference between a real Porsche Duck tail or a replica.  This is what I have found.
If I am incorrect in my research, please correct me. Â I am genuinely interested to know the difference between a real and a replica.
The  Duck Tail  from the 1973 Porsche 911 is one of the most iconic shapes in automotive history.  It is not only  beautiful but functional as well.   The duck tail provided lightness , better engine cooling, and decreases lift especially above 80 MPH and higher.  Ten years ago , I can remember seeing them for sale for $1,200 to $2,000 and thinking the seller was out of his mind.  Who would pay such a high price?  Well in hindsight,  I wish I was that fool.   Today , these Duck Tails can be $5,000 to $10,000 +.  Since the Porsche Company always pushed the limits of technology,  they experimented with fiberglass for aerodynamics and lightness.  The Duck Tails were not made of metal skins, they used fiberglass