Brake Fluid leak--Where????

Car is an 85 carrera.
It has had a brake fluid leak over the last few months that I can not find. About 2 months ago she went to the shop for the leak and I was told the rear calipers were leaking and they were rebuilt. Now the brakes work fine. No brake leak at all on the street over weeks- but in a 2day DE event- and it was driven hard- I had great brakes on the track, but I lost 1/2 a reservoir of fluid!
No fluid around the master cylinder, none in the vacuum boost housing, none in the stowaway where the AC blower and hardlines live. None in the tunnel in the car. I don't see anything near the calibers- all clean and dry. I haven't pulled the pads yet, I probably should to see if they are wet- but I am looking for a lot of fluid. I have had the system under 15-20lb of pressure for 24 hours- hoping that would show something--nothing, dry as a bone.
Any ideas of where to look- I am about ready to randomly start replacing things.
Thanks, sorry about the length.
Gary

WHen the brake pads where, the pedal will lower. Thus, the level of fluid will also drop. Where the pads new before the hard track driving? You say it was a two day event so I imagine there was a significant amount of track driving and braking. Although losing half of the fluid appears odd, it may be possibile.

I'm not so sure you would see any residue in the brake booster if the leak is occuring at the rear seal of the master cylinder. The engine vacuum is sucking the brake fluid out at a relatively high velocity ... if the leak is happening there!

I suggest removing, disassembling, and cleaning the master cylinder with 91% isopropyl alcohol, and I think you will find scuffed rear seal, and maybe a pitted master cylinder.

One note of importance: only Flare-Nut Wrenches should be used on brake system fittings, open-end wrenches or Vise-Grips will result in severely damaged fittings! Sears sells a nice set of Metric Flare Nut Wrenches, but you can save some money at Harbour Freight, though you will have to wait to get them.
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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 12-09-2000).]

I looked at the Harbor Freight flare nut wrenches (we have stores here) and they are junk. I'm a cheapskate but they are junk. I borrowed a set instead.

MC leaks are silent vacuum booster killers. The vacuum sucks the fluid out of the MC and it corrodes the heck out of the booster. And you don't see any brake fluid.

but you know, a guy showed me soem pads he had used at one track event (? days, one maybe) that were mostly worn! that wear volume times four would equal about half a reservoir.

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'83 SC

Thanks for the input.
The pads show a little wear- not enough to account for that much fluid.
Thanks for the info about the MC. I thought if the leak was at the MC seals I would see fluid there. That will be an easy place to start- the MC here is 15 years old, and probably deserves to leak.
thanks again
Gary