Gasket for flue passes?

Hi, I have a Vailiant boiler that needed cleaning. I took the 6 metal plates off the top to clean out the passes. They were really plugged up. There was some kind of gaskets on them but they just fell apart. My problem is I can't find anything online about the gaskets. I don't wanna run the boiler for fear of gases escaping. Any help will be appreciated. Thanks.