Mine came off to have both sills done, some clips broke, easy to fabricate some new stainless ones, as ford ones crap anyway.
If there is ANY rust on edges of lips tere will be loads more up above that's for sure.
One thing that really helps is ford having the sunroof drain in the sills, as when sill holes block up it overflows onto inside of car and rots out floor where your feet are.
tabetha