Sticky pad? There should be clips on the back of the mirror glass that engage that circular center piece. They can be a little tricky; different mirrors have to go in at different angles and whatnot to clip in. If there is an adhesive pad, it is likely just to dampen vibration...it's not what holds it in place.
You can probably get an entire mirror assembly for next to nothing (less than the glass from a dealer), but 1) you'd have to paint it, since it doesn't look like there is a removable painted 'cap' that can simply be swapped and 2) they are shitty. Fitment is 'meh' and the motors are cheap and loud.