My DC40 recently had a new internal hose fitted, the old one had split in half and as a result of the repair the vacuum effect was increased substantially back original level, so much so it was extremely difficult to use on carpets. Rather than taking rubber gasket out, I removed the head and found that it contained massive amounts of dust that prevented the rubber gasket working correctly. Once cleaned the vacuum worked like new, easy to push on carpets and cleaned effectively. I suspect the reduced vacuum effect over the years had lead to the build up of dust and debris in the head, once removed all was good.