This sounds like it really goes against the grain but... cut each end at a very slight angle- so that the leading edge of the rubber is very slightly wider than the rounded edge which sits in the chanel. Then.. the very end/edge of the rubber- the tip if you like that is usually the cause of the lines as it gets "nicked" cut a 45 degree flat on it. Just a tiny one, approx 1mm, just enough to take the point off the end of the leading edge. Although I use a wagtail flipper, this works brilliant for me, virtually no detailing and rubbers last much longer.

Do not attemp this with anything other than a brand new scraper blade though.