If you want to install the child seat tethers (which will bolt to the package tray structure), this is what you'll need for each tether location (there are 3 possible locations).

72 11 8 187 598 covering cap
72 11 1 922 499 screw
07 11 9 900 052 flat washer
72 11 8 187 599 support, child seat
72 11 8 187 601 bushing

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Instructions, per Jeff C (thanks!)

Sorry no Pics for the install - did this years ago. but I looked in the trunk, there are three bolt holes - threaded - between the third brake light holder and the seat. these are visible as they are in an indentation in the metal shelf and they protrude down from the rear metal deck about a quarter inch.

Thinking back, I shoved a wire upward (a small eyeglass screwdriver works well too) thru the hole, then on the inside I used an exacto knife and pushed it down into the hole. I seated the exacto knife till the blade engaged the hole then spun the blade around to try and trough out the material. The stuff is tough - had to also cut around the hole keeping the tip of the blade centered on the hole - almost like cutting grapefruit. You cut through the outer cloth on top of the deck, a thick tough foam like board and some sort of rubbery plastic membrane before hitting metal. Bring a vacuum cleaner or packing tape to clean up the chunks of foam. The thickness of all this is about a quarter inch. BMW thoughtfully manufacter a spacer that is about a quarter inch to act as support between the metal shelf and the top of the rear deck.

After the hole is big enough to fit the bolt - you still need to enlarge it to fit the metal spacer. Take the bolt off, attach the spacer and tighten the bolt to keep the spacer centered. You then cut round the spacer almost to size, a little smaller works too as you can just tighten the bolt and force the spacer into the soft deck material till it contacts the metal support shelf.

After it is fully seated - disassemble, insert the tether retainer on top of the spacer and tighten down. Finish off with the plastic cap and you are all done.