Oops, CRS strikes again!
I just doublechecked to make sure we have no black mark on the sill with the shim in place. No black mark. None. Nada. Then I began to wonder and I checked and found the shim is not there. I DID remove it and I DID put it back, like I said. But I guess I decided later it was better removed and I removed it. Or it fell off. Darn. Wish I could remember which it was. In any case, it's working fine without the shim.
Sorry for the confusion.