Check all four diaphragms for any sign of excess wear. Wear most often shows as cracks. Vacuum "leaks" through these cracks.

Purchase only as many diaphragms as you need; they are about $10.00 each.

The top diaphragms, facing up towards the bottom of the windows, are often the most worn due to more exposure to water and dirt that enter the door past the window scraper.

Before beginning, give the whole assembly a light cleaning. Mild soap and water is sufficient.