Defender clutch sticking mid way on return or release, please help...

Hello,
I have a defender 1986 12j engine. The clutch pedal seems to be ticking in the middle on return after engaging a gear but returns to normal every time I step on the pedal twice ( more like pumping). I tried bleeding the slave cylinder, it improved but only for a few days and the problem was back again.
The brake fluid in the reservoir has a dark colour close to the colour of used oil.

I have no idea what is about to go wrong or is wrong already. Somebody said it could be the bearing, gearbox needs to be dropped to replace it, someone else said it could be the master cylinder which needs replacing, please help.

leaky slave/master cylinder?

Just replace it dont cost much...

Is it easy to replace? is it a few bolts and nuts to tie?

Easy to replace, then bleed it. I imagine the dark colour of the clutch fluid is because of the seals in the slave cylinder breaking down. Can happen if the wrong fluid is used.

Yeah looks like one of the cylinders is giving up. Don't know which to start with.

slave is easiest i think two bolts and a pipe.
then bleed