The likely reason for the old one lifting is a combination of the damage under it and the posts holding it down being too tight (I had this on a WCS many years ago). I'd repair the damage on the left with some filler to give the new Cliffy something to sit on and then just put the new one on but don't over tighten the posts that hold it in place. If the damage is such that you can see it with the Cliffy on then you'll want to look at doing some touch up 
