master cylinder problem?

Ive just replaced the clutch slave cylinder on my sd as it started to piss oil out.
Fitted a new oberon unit. bled fluid through. all seemed good.
Now if i keep the lever pulled in, i lose pressure, and the resevior level goes up.
so im guessing the master has also gone?
Ive bled the master too, but im 99% sure that the level in the resevoir going up as i lose pressure is a give away.

Anyone?

Yes I guess it's fooked. The master cylinder only bleeds back when the lever is all the way out. There is a small hole to allow oil to go in the line when out but when you squeeze the lever it gets closed off by the plunger. Either the plunger is worn or the seal.