about 6months ago i changed the master and cylinder due to a slow leak that caused my clutch pedal to feel mushy and not disengage the clutch. About two weeks ago i looked at the brake fluid reservoir and it was well below the minimum level of the brake fluid level. Could it be that the clutch line sucked in air and thats whats causing the clutch to not feel normal, or could the actual slave cylinder be failing again?

 

First choice sounds most likely. Look for brake fluid leaking at the input or output slave or a dropping
level after refilling for evidence of the second choice, though.

 

If you had everything apart, air in system is a possibility, it is a temperamental bleed procedure. Even replacing the slave alone can end up in you bleeding the system twice to get proper pedal pressure and engagement.

How do your brakes look? Low pad material will result in more fluid being required to move the piston to engage brakes, you could be in need of brakes.

I assume there are no leaks, brake pedal doesn't fade with moderate pressure?

Just to check the easy stuff, pull the boots back on the slave and master to check for fluid leaks. If either are leaking then replace them, again. If they are MINI OE parts they have a 2 year unlimited mile warranty on them regardless of installer.