New Member with a dirty rear window

[Horseshoe Bay X5]

Hi All:
I am the proud owner of a new 2011 X5 35d Premium package here in Vancouver and am very happy to find the active member's site. I notice that the rear window quickly gets covered in dirt and grime from wet and slushy roads and the poor rear windshield wiper struggles to keep up.

It looks like the culprit is the rear window spoiler creating a vacuum that sucks up all the sludge and grime which promptly deposits itself on the rear window and upper rear brake lights.

Has anyone experimented with deflectors on the rear window spoiler to create turbulence that would minimize the low pressure/vacuum behind the vehicle? I don't think it would take too much - kind of like the deflectors on aircraft wings to eliminate vortexes.

As I don't ever speed () I am not too concerned about any instability this might cause!

Failing this are there any other solutions that work?

All he best

Joe