Has anyone found anything that reduces the dust collection on the hip and rear window? I tried spacers on the mounting bolts but that little extra height didn't achieve anything worthwhile, if anything at all.

An available roof wing that mounts on top of the spoiler probably works but I'm not fussed with the price of around $1,000 nor the looks. A hip lip spoiler is also available but I suspect that would only act as a dust collection shelf but perhaps works when used in conjunction with the roof spoiler.

On my L322 I cut holes in a spare spoiler and mounted a sunroof wind deflector reversed to act as a scoop which did quite a good job. It was barely visible due to the L322's height but unlikely to be similar on the L405.