Never heard about the cables being "brittle" although they are a pain in the arse to fit connections too from what I've heard.
They have a kind of kevlar lining I think with a plastic inner, supposedly making them significantly stronger than standard Magura plastic lines.
What you say about the cleaning out is definitely true, a lot of the early Denguras ( not sure if its the same with the new ones ) had problems with swarf not being removed from the barrel. When used this caused scoring inside and thus leaks.
Ye, cheaper on here though once you're validated You'll probably only have to buy a couple of bits to get yours going again anyway.