Master cylinder leaking at top

[TN Mopar]

I have an annoying problem that I am tired of living with
My Master cylinder leaks out the top underneath the cap
I have tried changing the Masters, I have run the Master as low as half full
I have bent the retention strap until it is so tight I can barely snap it over the cover
I have googled this and not really found a definitive answer

At this point I am going to change the Master to the Mopar aluminum type with plastic body

Has anyone had this problem?
Will the new style Master fix the leaking?

and lastly is there a Wilwood Master that will work?
something fancier than the plastic and aluminum

The car is my 66 Charger with spindles and rotors from a 73 Dart
I used later model FMJ rear hung calipers (slide not pin)
The Master is a quality MAster from Right Stuif 15/16ths bore
Everything works well except the sl;ow leak out the front of the Master and it has damaged some paint

 

[MIKESPOLARA]

You replaced entire master and cap with a new one and it also leaks?

 

[hunt2elk]

If you go with the newer style aluminum cylinder, buy a set of Dorman replacement caps and seals right away. I have 3 of them and they all leaked after very little driving. The Doeman stuff recommended by Dr Diff took care of the problem.

 

[VANDAN]

Make sure the gasket surface is flat & clean, You should be set...

 

[TN Mopar]

You replaced entire master and cap with a new one and it also leaks?

yep
2 fer 2

 

[padam]

If you go with the newer style aluminum cylinder, buy a set of Dorman replacement caps and seals right away. I have 3 of them and they all leaked after very little driving. The Doeman stuff recommended by Dr Diff took care of the problem.

Tried these they still leak

 

[TN Mopar]

is there a Wilwood master that wont leak?

 

[MIKESPOLARA]

I take it you changed to a dual master.
When I use to sell masters/boosters ( not for Mopar) I had the same problem occasionally. I found in shipping a few of the masters would get a very slight "bend" in the cap due to the weight of the package, maybe 8-10 masters packed in one box. This was shipped from manufactuer to me. The constant pounding boxes get when shipped with UPS/Fedex,freight etc would cause some masters to pound on the box below it. The damage was mostly unnoticeable but upon careful inspection I noticed the almost invisable dent on the cap. No matter what I tried that cap would never stop leaking. The tweek in the cap made for a deformation in the sealing area and can not be straightened no matter how much I tried. I then had to keep extra caps on hand to replace any suspects. This would happen maybe 1 out of 20-30 masters so it wasn't something that was real noticable.
Can you source a new cap alone? If not buy a master from a different source

 

[Potts]

Take off the cap, wipe it dry, then apply a THIN bead of RTV black on the rubber underside of the cap where it touches the master.
Let that RTV dry, wipe the master cylinder surface dry then re install cap.
Mine stopped leaking after this application, just don't mess with it too much after that.
Really no reason to keep checking the fluid too often.
You'll be able to tell if the fluid is getting low .