Hi Manfred.
You are right about the no duty for 20+ year old cards but, that is for North American made cars. Because the Porsche is from Deutchland, there is a 6.1% duty. Some Customs Officers forget about Porsches being European cars and do not charge the 6.1%.
I'm new to this Porsche game and have been getting a lot of stuff from eBay. I also found a guy in Toronto who has many parts and has some US connections. His name is Frank
911parts@sympatico.ca . Tell him I sent you.
Randy