I have an American Standard Plebe 4083 L85 toilet. When I went to replace the tank to bowl gasket I noticed it does not have a cone shaped gasket like sold in stores. When I try to use this cone gasket the tank sits up real high and rocks because it is unable to meet the bowl. I have been to plumbing supply houses and they say this is the only gasket used. This gasket has never been replaced and I have three of these toilets that have the same gaskets since new. Has anyone seen this or replaced this type of gasket or know where I can get one?