The gasket that was on the nut for the opening ripped off last night when I opened it to check the levels (empty!). It was the first time the master had been opened in a decade so it basically ripped apart. I am having issues finding a replacement gasket as everything seems to be susceptible to Dot 3 fluid. Is it required or can it be metal on metal? I'm thinking something should be there to prevent extra air getting into the system. If its required what have you used if you were not able to source the actual part from anywhere?

1958 Chev Apache 3600