A 75 911S motor w CIS has a few Polyamid lines with a rubber outer sheath, so they appear to be hoses but they are not. The plain poly tube is readily available, the rubber sheathed line is much harder to find or purchase. I have some on order from Gemany, and still don't know when it will arrive.
Polyamid (plastic) lines are very durable, even with the new Ethanol fuels. If left alone, they will last the life of the car. When disturbed they begin to loosen at the fitting. If kinked they will fail.
I have been making replacement Porsche fuel & oil hose assemblies for many years, but only recently started doing the CIS lines.
If I could replace all the rubber hoses in a Porsche with Polyamid lines I would do that. Porsche began this with the 964 models and just about all vehicles built worldwide today use some sort of Polyamid or plastic lines wherever possible.
Len