Help confirming clutch malfunction please!

I posted just before Xmas about my clutch master going, so I changed it out and had good results for a week or so, but now the problem's back again! Can anyone help me by confirming my diagnosis please? (93 XJ, AX15, internal slave)

I'm getting reducing pressure at the pedal which builds up slightly overnight. Since I replaced the master, I think I might have just got a duff one - I got a Lucas one which is a like for like with the one that came out, so OEM I suppose.

Clutch master cylinder is faulty if:
No leaks but pressure at pedal drops off
Leaks from back of piston onto fuse panel

Slave cylinder faulty if:
It's leaking.

Other problems could be with the pipe if that's breaking down. It's not, as the line's not near to the manfold.

Sorry about the long post, but I'm really getting fed up with this particular problem, and need some sane advice from people who know jeeps!

TIA

Quick update:

I've been advised to bleed the system again to see if I can get pressure back, since it's possible to have a small leak coming from somewhere and not have visible fluid loss, particularly if the drain hole at the bottom of the bellhousing has become blocked. Does this sound plausible?

Yep, I was having the same problem and somebody told me that too.

What did you do to fix it? It seems as though I'd be better off just replacing everything, rather than chasing down the problem bit-by-bit.