The conclusion I've drawn concerning this is that the heavier fender extenders tend to crack the fender just as you have described. I use an extender myself but it's a lighter, plastic one called the Fenda Extenda made by Pyramid Plastics. So far, this has worked out just fine. I have friends running these and they have had no problems either. I do believe the extender is useful in protecting the front of the engine so I plan to keep using it.
I have the same, Fenda Extenda. It's been on the bike for over a year with no signs of cracks to the fender.
KJ
SOLD 2013 F6B Black Deluxe
2014 Victory Cross Country Tour EZRIDE
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