I can't find the receipt but I had to buy a new guard liner for my car when I first got it as the passenger side was missing completely. Only cost about $120 from Subaru from memory.

Maybe I exaggerated about the liner sitting loose on the tyre. Although the edge of the liner does sit loose, the plastic is pretty stiff so it doesn't sag. Only if you had a really low car and you pumped the guards out would it touch and even then it would only be under heavy suspension compression. My car was a bit low at one stage and it did rub a little on one side but I've since raised it ever so slightly and have no dramas.

If you are concerned, a solution may be to heat and stretch the plastic liner so it lines up with the guard. I'm sure this wouldn't be too difficult?