If the crack runs close to the stressed bolt-on area then give up. Unless I miss my guess most of those parts are polypropylene or soft abs and not gluable unless you buy the 3M specialty glue at like $80/tube. Oily base plastics absolutely suck to repair under most circumstances, nothing sticks firmly to the plastic because it constantly lets off VOCs out of it. I've pulled it off a time or two if the cross section is thick or well-supported but never like on a fender.
Pics rule in things like this, can determine yes or no. Depends on how big and vicious the crack is. Like saying my car is broke, what's wrong with it?