One of the holy grails of 3D printing is TPU (or any flexible filament) that can withstand heat and gasoline vapor. Thousands, if not millions, of cool old motorcycles are sidelined simply because the boots between the cylinder head and carburetors, and between the airbox and carbs, are "perished" and replacements are simply not available at any price.
So far, experiments in this direction have been spotty and disappointing.
Overall, being able to print flexible gaskets that could withstand heat, antifreeze, oil, gasoline, diesel, etc. would be an absolute boon for all kinds of mechanickers, but I don't know of much success in that direction.
Gaskets that can be custom cut from sheet have been around for years. but many applications require a specific molded shape.