I once purchased a set of hard to find NOS foam rubber tail light lens gaskets for an old British car. They were decades old, and absolutely worthless because the foam had deteriorated to the point of crumbling into fragments just by handling them. I tried duplicating them using a modern urethane foam (and the techniques described in the article), and that sort of worked, but in the end they were just a poor design with significant shortcomings. Then I was struck with an aha moment: what about 3D printing? I have printed many custom plastic car parts in recent years, so why not gaskets? I designed an improved configuration with a raised lip around the edge to keep it positioned correctly on the lens (an advantage of a 3D gasket as opposed to a flat one), and printed it in a soft rubberlike urethane material. The result looked and performed far better that the original.
For making flat gaskets, another option is one of those cutting machines like a Cricut Maker. Looks sort of like an inkjet printer, and cuts thin sheet materials with great speed and precision using a computer generated pattern. You can also cut vinyl graphics with it.
Computers and their associated peripherals have become a fundamental part of many hobbies in recent years, and the old car hobby should be no exception!