Carburetor Gaskets

How important is it to replace the top cap gasket on Mikuni VM28SC carburetors, I’m going to clean up the carbs and replace the float bowl gaskets but if the top cap gaskets are in good shape should I still replace them? What purpose do they serve, if they leak will that effect performance or are they more for keeping dust and dirt out? I have not seen them offered from the on-line Z1 parts suppliers other than in carb rebuild kits which leads me to believe they might be that critical.

as long as they arent torn up reuse them

I think I have been using the same float bowl gaskets for 25 years now.