That's what always work for me as well daddio. I'd try that Mike - the extra venting gives that bouncing air somewhere to go.
Interesting though that a W210 exhibits that behaviour. I'd expect it from my W115, but the W124 actually buffets very little even at freeway speeds....
'95 E420 - 'Shadowfax
'92 Volvo 740Turbo Bard
'74 240D - 'Ol' Green
' 4spd Manual 104kmi. (sold
'77 300D - 'Red
' 223kmi (sold)
'75 240D - 'Bianca the Blue Bomber