Brainstorming: Try making some sort of adapter for your vacuum cleaner hose and close the other vents and see if you can dislodge or move the blade around any to try and get a better look at it. The adapter could cover the whole vent or use a small one and slide it down the hole. Is it making noise when the defroster is on?
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (194,000)
1999 E300 Turbodiesel (244,000 miles, dies at 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles)
2011 Audi A4 Avant (129,000 miles) hate this car!
BMW 330 xi 6 speed manual (100,034 miles)