If level correct and was not overfilled before, presume you can assume no bad leaks (a small slave cyl clutch leak letting air in won't always show much in level, thats a fairly big master reservoir)
So best thing now is get it bled, can do this:
1) without any tube
2) with a simple tube into a jar with some fluid already in, end below surface
3) with a bleeding tube (any motofax) having a one-way valve at the end
4) with a pressure bleeder, pumping up master reservoir.
For now, if you haven't the tubes, the technique (1) is:
1)Wheel off, jack stands, to get good accces;
2) jam up operating lever (helps);
3) loosen bleed nipple (good fitting ring spanner), then just nip back up putting some old cloth around area in readiness (Rem! gogs/eyes!);
4) call out to helper ' DOWN' - helper pushes smoothly, evenly to floor and holds there, whilst you loosen bleed screw as pressure comes on;
5) helper repeats 'DOWN' call when pedal hits the floor at which you quickly nip it back up, calling 'UP', when you have done so;
5a) helper repeats 'UP, when pedal back up, so you know you can then get spanner ready and call 'DOWN' again (try to leave ring spanner in a good position to nip and open bleed nipple enough to bleed a good stream in one turn without removing from nipple)
6) repeat... 4 & 5 till fluid issuing forth without air bubbles or spluttering each time you call 'DOWN' and loosen nipple. Maybe until clean fluid coming out.
7) Check and top up reservoir if noticeably down from max. (no need at each repeat of 4&5
Consider whether you have achieved 6) I so remove jam! (helper should never need to, or stand on pedal hard.)
9) Call DOWN and observe op lever travel... is it moving a decent amount (as discussed earlier)
10) Does clutch now work better
11) Does clutch continue to work better or does it quickly degrade again
12) Pop rubber bellows off slave cylinder to see if fluid is escaping around pushrod/piston. Ditto master cylinder, though should be pretty obvious by now if its.
13) Good luck..
