Here is the kit I used just a week ago to reattach my mirror on the wagon. I've used the same stuff a couple other times on different cars over the years. Works great and is only $3.99 at O'reilly.
Follow the directions to the letter! Only use a drop as it says. Make sure the button and windshield is clean. I used a safety razor blade, followed by denatured alcohol to clean mine, and then wiped it really good with a clean paper towel making sure it was 100% clean and dry, before using the cleaner/activator pad that comes in the kit. It is very important that the temperature is within the range shown in the instructions. I applied mine at 70° F. I let it sit for an hour or so before hanging the mirror on the button.