Real annoying but often the leak is coming from an area different from where it appears.
In addition to removing the sill plate, pull the fuse panel door on the end of the dash and kick plate over the brake handle and check for water in those areas......then the leak is from the sun roof channel, windshield or OnStar antenna, possibly even the roof rack. Originally there was water behind the fuse panel area and dealer's sealing the windshield fixed that area, but evidently that was not the only leak because there was still water coming in at the in the sill area and under the driver's rug.
On the second trip to the dealer they glued in the seal on the body frame going around the drivers door and that fixed the leak because there was no more in the seal area.....evidently it was channeling water from the roof area under the inside of the seal and out the seam located at the sill plate.....but even though they stopped the leak.......the padding under the rug was soaked with about a quart of water from the leaks that just sits there and the rubber mat keeps it there and the pad wicks the water all the way up to the pedal area even though the water was coming in at the bottom area where the door body seal is seamed and getting into the wiring channel and getting sucked into the rug padding.............had to go through four rolls of paper toweling and pressing on the carpet and following up with a hairdryer to get MOST of the water out, then no rubber mat for a month and finally the area dried up and it continues to remain bone dry so now I can say for certain there are no more leaks.