While bleading my brakes...

I've seen that on a BB clutch master. It was a bear to catch. The rubber grommets between master cyl / reservoir were available for that, those might be the same parts for the brake master.

 

If it is the grommets be very careful when you pull up on the reservoir,it's easy to crack the nipples on the reservoir.A replacement will cost around $400.00.

 

Contact Speed Works he can get you a reservoir if yours breaks.I found that if you pull straight up try not to pull at an angle it will pop off.You have to pull up pretty hard.The first picture shows a bad seal,I found replacements on Ebay,not an easy task.If memory serves me they are 24MM.I have a spare Master Cylinder if your's cannot be rebuilt.A new one is around $700.00 at T-Rutlands,Good Luck!
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Richard, if you're taking out the MC then let all the brake lines drain out. What's left in the resevoir won't leak out during removal. If you want to be sure then either a) pump it out with the pedal as you suggest, or b) stick a rubber plug in the f/r outlet ports.

I found that it was difficult to get the resevoir off the MC while in the car - awkward position/no leverage, thus I removed it as a unit. The back two nuts are not easy to remove but if you use an extension slightly longer than the MC itself you're able to swing the socket wrench somewhat to loosen/remove them. Removing the resevoir on the bench wasn't too bad - squirted a little WD40 around the rubber grommets and let it soak in for an hour or so and popped the resevoir straight up with moderate hand pressure.

Going back in it's easiest to bolt the MC back in with the resevoir removed, then push the resevoir down into the grommets afterwards (so that access to the rear 2 nuts is easier) - doing so doesn't require much pressure.

The MC is a very rare benditalia and hard to come by. If the bore of yours is pitted in the least then don't bother just putting it back together with new seals - it will leak. There are places (www.goldlinebrakes.com for example) that can install a nice brass or ss sleeve that'll make it better than new (won't corrode).

The MC rebuild kit from superformance in the UK is pretty good and not expensive (can't say the same for the caliper rebuild kits, which are junk).

Good luck!

 

Not for nothin', but did you try bleeding the other calipers again and see if you got air bubbles there too? I've seen it happen that if you loosen the bleed screw too much, it will suck in air around the threads and push it out the bleed valve, so it looks like you have air in the line. You should be breaking the bleed screw open only about a 1/4 turn. Before going and tearing the car apart, go back and try rebleeding and see what happens. If you get air out of all of them, then obviously, it points to another problem. Just a thought to possibly save you some work.

 

When I drained my reservoir i used a turkey baster,No mess put the soak pads down for insurance.And yes the Master Cylinder is easier to remove this way.

 

I would drain all the fluid. Its hydroscopic and with open ended lines, at the master cylinder end, will absorb a lot of moisture from the air. That's especially the case should it take a while to get the cylinder done and back in place.
Moisture in the fluid substantially lowers its boiling point with obvious negative results.