Leaky MC Cap

I have the apparently common leak around the edges of the cap from my 68 Barracuda master cylinder. The master cylinder is for disk front and drum rear, with the 2 different size reservoirs for front/rear. It weeps around the cap/gasket surface, enough for to cause the OEM style cast master cylinder to have surface rust and a few drops have damaged the paint on my detailed engine bay:mad:

I keep the fluid level about 3/8" below the edge of the reservoir. The master cylinder sealing surface is flat by straight edge with no visible defects. The gasket appears to be intact.

I'd like to try replacing the cap/gasket before i go through the trouble and cost of replacing the entire master cylinder. Does anyone have a part# or link for the correct cap and gasket?

Any other suggestions for sealing this type of master cylinder other than just replacing it with one that uses a screw on cap for the reservoir? I hoped there might be some kind of gasket sealant that could be applied to the edge of the sealing surface, but I think brake fluid destroys everything.