Prairie ghost: Is there something sacred about the screws that came with the pad? Why not use standard screws? They will be hidden when the job is complete.

From your comments above it seems that your pilot holes are not deep enough or the correct size. I have had this problem with plugged holes and it has always been the depth of the hole and another 64th in the drill size.

I think that Damascus has given you awfully good advice.

Just my 2 cents. R.