could this be a preformed gasket ? or just a sticky glue strip on the flares ... there is automotive double sided tape available from places like cdn tire brand="seal it" etc for reattaching trim BUT all the ones I've noticed are several mm thicker than what I imagine your refering to and wouldnt follow contours easily ...
ie: might be an eyesore fix ...
my yj doesnt appear to have anything I can see between those two surfaces ...
which jeep are you refering to or did I miss that ...