I don’t know if the slit thingy has a mekor or not but let me explain the point:
It doesn’t matter if the skirt is perfectly tznius and the slit doesn’t come over the knee..the point is that it’s ATTRACTIVE nontheless. It attracts the movement of the legs.
Same with the other issues you bought up. perfume – if someone is heavily perfumed no doubt about it, ppl in the street will turn around for another glimpse..
And bright colored clothing easily catches the eye.
Just like in Mitzrayim the yidden were saved bezchus the nashim, same holds true for the upcoming geula (may it come speedily). Women have such a special tafkid and chiyuv..why r we arguing about mekoros?? When it comes to laws of tznius, not everything is written in black and white. You need to use a good deal of judgement. Besides there ARE plenty of books with excellent mekoros out there..