spoiler installation
great thread on the installation. I got my spoiler off ebay as well from carparts123.
PAINTED 2008+ 08 Scion XB Factory Rear Wing Spoiler | eBay
I asked the supplier if there was 2 or 4 bolts holding the unit on before making the purchase. They replied that 4 bolts were. I chose this supplier b/c ad said it came with install instructions and video.
When it arrived only 2 mounting bolts were on the unit i received. None of the promised instructions were included in the box, so i went back to the ebay ad for guidance on how to mount it

for their instructions on spoiler installation. I took about 30 minutes to study the instructions and about 25 minutes to do the measurements and fit-up prior to drilling. That was the hard part..... actually drilling the holes in a perfectly good tailgate. I installed it anyway with 2 bolts and i like the end result just fine. The ad describes it as having adhesive on the rubber cushion surface with a peel-off tape cover. My unit did not have this either.

It has a real thick rubber cushion on each corner that compresses slightly when the screws are torqued down.
I'll post some pics when i figure out how that is done.