Master cylinder faulty?

[SharkGill]

IMG_8975.jpg
I lost brake pressure the other day so thought it's time to do the rear discs and pads as the car has been asking for a while.
I've just noticed leaking brake fluid from between the reservoir and cylinder. The seals between the reservoir and cylinder have perished and I will be collecting new ones from bmw tomorrow.

I'm just wondering could the actual cylinder be faulty or are perished seals enough to cause this sort of leak?

[shogun]

Usually just the 2 plugs 34311163464, if you are lucky. If you lost brake pressure, then maybe the expansion tank was completely empty and air came into the brake system.

[SharkGill]

I did the rear discs, pads and replaced the two plugs on the reservoir. I have a brake fluid bleeding/flushing tool which connects to the reservoir and replaces old fluid with new as each calliper is bled but for some reason this device wouldn't work even though it had a pressure of 28psi. So will have to flush the fluid when I have an assistant