Brake Fluid Leaking From Master Cylinder Lid...WHY ??

Moparts please help>... I cant seem to stop brake fluid from leaking from master cylinder metal lid. 69/70 superbee with 4-wheel drum brakes. I've replaced 3 master cylinders, proportioning valve, and bench bled all masters. rubber gasket isnt squished or torn. this is the bolt on style lid. only used until 1970. in 1971 the design changed to the Bail Strap style lid. no more bolt. Car drives and stops great doesnt seem to have air in it. pedal feels great. please help its ruining my new paint job and undercariage. :bawling

the gasket surface should be treated as any other
no blemishes .nicks or the such..often the lid is warped just like valve covers...cranked down to tight to many times..i often take a orbital sander to the tops

thanks ramman, i ordered a couple more masters to get the lids and gaskets. just in case !!!

I had that problem on a new master. It leaked at the front. Turns out the wire bail wasn't evenly tight. I tightened up the bend at the front of the bail and the leak is stopped.

Are you over filling it?...just a thought!

....in the meantime. Switch to DOT5 silicone brake fluid.

I had the same issue. My friend came up with using two rubber gaskets - modifying the second one to fit on top of the first. No leaks since then.

thanks guys, i thought of the same fix cutting an outer ring of rubber and shimming the lid gasket...double them up to give them more squish. and who thought this bolt style lid was a gud idea? its a pain when constantly adding fluid during bleeding procedure. the inventor should be shot...ha