just an update:
i guess i remodeled that part about 20 times. i find it's often best not to model just half of it and then mirror it. the curvatures won't flow nicely over the mirror plane, even if i model surfaces on the mirror plane and tell the other surfaces to be either curvature continuous to these surfaces or normal to the sketches.
i also sometimes create a driving sketch cosisting of multiple sketches and instead of using a compound curve to make surfaces of it, i use 'fit spline'. that gives me one relativley clean curve to make my surfaces with. when knitting these surfaces i then sometimes have to merge gaps, as the fit spline is not 100% accurate..but it's sometimes the better solution.