Toilet blade seal leak

I have a 22 year old Thetford Aqua Magic with that blade seal. As Bud said make a tool that you can insert into the seal groove to clean out any debris that gets caught there. I just did this yesterday for about the 3rd time over the years to clean out the groove. Just checked this morning and it is still holding water. Also the spring could get weak and not close all the way so you may need to help it up with your foot. Another problem I had was that hard scale built up on the under side of the blade from hard water and had to be scraped off and sanded to get a smooth surface for the rubber seal.