[dataway]

Below are some photos of a sudden leak that has developed at the rear of the OEM MC on my 68 GTO.

Fluid has been in this MC for several years with no leaks. Previously the car stayed in a garage with very stable temps around 55 degrees. The last 18 months it's been in new building where the temps have varied between low 40's and 70's, and higher humidity. It is filled with DOT 3 fluid.

At first I thought it was from the rear seal of the MC, but from the photos I can see that it's coming from either the back of the cap, or maybe the the hole where the wire loom inserts. What I don't understand is the fluid will leak down to where the rear reservoir is almost empty (without driving the car), the front reservoir remains full.

Surely the capillary attraction of brake fluid is not so high that it climbs out of this reservoir and out the rear cap seal? The leak does appear to be coming from high in the back, right in the area of the MC cap seal tab that goes through the cap.

Cap goes on tight, zero leaks in the lines and fittings. I haven't open the MC in a couple of years at least, never leaked a drop until the last month or so, even though I'm not driving it.

Thanks,

BTW .. what is the hole for at the bottom of the MC? Mounting a proportioning valve?