Clutch master cylinder replacement

quick question,

I'm losing pedal on the clutch again, dropping and staying down and even when pulled back up only having feel on the last inch or two, so i reckon its the master that's gone, i have bled it numerous times now and that gets some feel back but it doesn't last long and i noticed on the last bleed that the fluid is coming through aerated, well it looks aerated its gone milky but left in the jar after bleeding it goes clear. so is this a fooked master or should i be looking at anything else first?

I replaced the slave about a 12k kms ago and that helped with the problem but as there is air in the fluid when it gets to the slave im thinking the problem is upstream of the slave and that only leaves the master as far as i know as the damper wouldn't introduce such fine aeration would it?

all input appreciated.

Ta

If the rubber lets fluid by,you lose pedal "push"(foaming in reservoir is a clue).In the past I have taken master cylinder's apart and cleaned crap off the bores and made them go again.I believe you can get some additive to make the rubber swell-might be worth a try,but at the end of the day a new master is best solution.Presumably you have a decent length of slave rod hanging out of gearbox,ie fork not punching through