Mine isn't broke or cracked but the prev owner at some point just had the wipers going and going wearing marks into the glass.
http://imageshack.com/a/img801/7940/dsc03283f.jpgI've seen the Eastwood kits for polishing glass, but I would think that (depending on how deep the grooves are)it would still leave a 'trail' after it's finished that the 'new' wiper wouldn't pick up.
I've sold Amsoil products for years and have RAIN CLEAR that is similar to RainX, but lasts lots longer.
SO, if I attempt a 'polishing' and mess it up, are there still glass companies that make a curved glass and a good seal for them also.
I've done the soapy string and boiling the seal to soften it, but MAN, that was decades ago!!
Unless they randomly make a batch every so often.
Errol