Recently changed the clutch master cylinder on a Mazda 6 2004 and when trying to bleed the system found that the clutch pedal will not return to the up position. Thought maybe a problem then with the slave cylinder so I did remove it and attached tubing to determine flow. Still had air mixed into the flow however there is fluid flow. Should the clutch pedal not return to normal (up) position from the spring resistance in the master? Slave cylinder seems to have no leaks but can probably use replacement. I noticed though that the clutch fork was pretty much stiff to push. Can the clutch fork be moved by hand (fingers) or should the resistance be too great? If the clutch fork indicates a finished clutch I don’t see any point in continuing as the repair value may exceed the car value. One other question - with the slave removed there was no fluid dripping from the hydraulic line with the clutch pedal down but when I manually raised the pedal it was a constant drip. Does this indicate a leak in the system between reservoir and slave or just normal gravity affect?
Should the clutch pedal not return to normal (up) position from the spring resistance in the master?
If it has been correctly bled, it should return on its own. If you didn't bench bleed, it may not be able to draw enough fluid to get started on its own. In that case, not returning is normal.
Based on your "air mixed in," comment, it either hasn't been bled enough yet, or it needed the bench bleed from the get go. In my experience with skipping bench bleeds, you can maybe recover by manually pulling the pedal up and pumping it to build pressure before you crack the bleeder. The pedal will be jello for a while until it fairly suddenly stiffens. This could take a quarter of a bottle of hydraulic fluid or more, so weigh it against how hard it is to get the master in/out. If this was for brakes, I wouldn't recommend this at all.
Only because I do it wrong every time, are you sure you have the right bleeding procedure? Reservoir cap off, Pedal down>crack bleeder>let fluid run out>close bleeder>pedal up. Dip your bleeder hose into fluid so it can't suck air back in, don't let the reservoir run low.
Can the clutch fork be moved by hand (fingers) or should the resistance be too great?
Not unless you are a gorilla. It might wiggle a bit.
I don't know enough about the internal workings of the self adjusting pressure plate to say whether or not the fork tells us anything about remaining clutch life. I'm guessing it doesn't, otherwise they could put some nice factory marking on the bellhousing to indicate clutch life remaining.
Does this indicate a leak in the system between reservoir and slave or just normal gravity affect?
Seems like normal gravity to me. You had a straw with your thumb on the end (pedal down). You took your thumb off (pedal up) and the fluid came out. Depending on the internal design of the cylinder, you could leak straight from the reservoir this way.
One last thing to consider: usually the master to slave line is a hardline. There is a seal/gasket where the cylinder and the hardline mate, and the gasket likes to stay behind in the old cylinder. The mating could seal well enough without the gasket that your clutch will feel normal during the bleed, and fall to the floor when you go out to drive it in the morning. Its hard to see the leak if you already got hydraulic fluid everywhere taking the old cylinder out.