the abs plastic the replica kits are made out of is like more brittle than your side skirts. your side skirts are a plastic/eurethane blend. they're alot more flexible.

if you could imagine purposefully bending the hell out of your side skirt it would bend and leave a warp in it. eurethane would bend but bounce back more like rubber still leaving a knot from the bend. if abs didn't crack in half you'd be very lucky.

another thing is with eurethane you can kind of stretch it to make it fit perfectly snug. with abs plastic if it doesn't fit right it probably never will.

this is why I try to stay away from the $100 replica lips.