Loose Rubber Thingy

Only photograph taken today. Explanation below.
Today has been much less busy. Marlane was up most of the night with her mother so it was very quiet this morning. After Jonty woke me at 5.30 I fed him, let him outside and then we both, Jonty and I, slept until 9.00, couldn't believe it!
I took the bike out to go to Wilko store for bird feed. We were completely out so got a 4kg bag of Sunflower hearts and 4kg bag of peanuts. That should last even our garden birds a little while. Also bought a new feeder for the peanuts, the old one is looking very unhygienic and is difficult to clean. Popped into our local pharmacy to pick up a pain easing  prescription for Betty. A very cold ride but it wasn't far.
When I got home I noticed the rubber, around the air filter, had vibrated loose. It doesn't stay on very well at the best of times so I'm looking for a solution. I could just leave it off but I think it just doesn't look right without it. Might try some sealant around the grove. Someone on the H.D. Facebook Page suggested black Gasket Sealant. Just looked it up on ebay and it's only £5.50 for a tube so I'll give that a try.
It was on the same air filter cover since I bought the bike and is only loose since the air filter was changed to 'Screamin' Eagle' to work with the same name exhaust. Can't think of any reason for it to be loose but loose it is!