Ive always had bad luck with leaky master cylinders. I will tighten the bail to ensure a great tight fit, and darn it, fluid still will come out of the top. This past restoration I took the master cyl, and out of the truck, fliped it and sanded the surface on a flat board with sand paper to ensure that it was true. With a new chrome lid on it, the thing leaks like crazy, I have to keep it only 3/4 full at most, and I still get some coming out.
Any sure fixes for this problem on mopars cast iron dual master cylinders? If not, someone needs to invent something.

fish

A board is anything but flat , try it on a formica counter or better yet a surface plate.

Loose the chrome cover .

I have dealt with the same thing with my 72 Duster. I've tried different covers, different rubber seals, different spring retainers. My brakes work fantastic, but the seeping fluid is annoying. The machined surface on my M/C isn't pitted either.

I got sick of this too with the factory cast cylinder. Makes it impossible to keep it painted and looking somewhat nice.

Probably not what you are going to want to do but just throwing it out there. I went with the aluminum MP 2 bolt master cylinder with the screw on caps/rubber seals and stays pretty dry if you don't ovefill the resevoir. Also, resevoir is plastic and body is cast aluminum so no rust!

This and the 4 bolt-2bolt adapter plate and it bolted right on to the OEM booster.

I had same problem just added another gasket inside of the other hasn't leaked in two years.

I used a very thin layer of the gray "Form a Gasket". It hasn't leaked a drop since.

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I had same problem just added another gasket inside of the other hasn't leaked in two years.

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Yup. I have done this on several vehicles and it has worked great.

Stan

I just had the same problem . I tried two different similar covers and it still leaked,bought new master cylinder and no more leak

I found that if I don't have my cover perfectly centered (front-back, left-right) that the fluid tends to weep.

When it's centered, no leaks. The lid will likely want to readjust on you when you slide the wire bail over the top so you have to make sure you don't loose the centered position when securing.

If you have more than one lid, you may try and find the one that has the least amount of slop.

I had a new MC that was a leaker and found the tension on the bail was less on one end. I adjusted (bent) it and leak fixed.

Had repeated problems with my current master cylinder. Replaced gasket, tried two gaskets, and filed sealing surface to no avail. Decided to bend (tighten) the bail in my vice and reinstall. Has not leaked since, going on about two years.
Ron