I believe he's talking about a lip spoiler to add to the factory one on the hatch lid. Such as this:

Painted BMW E53 x5 Trunk Spoiler Rear Wing 01 02 03 04 06 § | eBay

Vivid Racing wants $825 for the official AC Schnitzer version, and I don't even think that is painted:

AC Schnitzer Roof Spoiler BMW E53 X5 99-07

That little ACS sticker is quite pricey. But I heard the ACS version adds 50 HP and enough downforce to take hairpin turns at 100 MPH+.

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