could be a worn pressure plate, but first i'd flush the fluid and check the adjustment. you'll want to do this anyway, since the fluid's black, so you may as well do it first, and see if thats the problem before you drop your transmission. the pressure plate is supposed to last the life of the clutch, but it's not always going to, and sometimes people reuse them with a new clutch plate.
its always best to buy the kit and replace all the components at once so you dont have to get back in there.
if you have a seal problem, normally they leak, and if the master or the slave are about to go, flushing the fluid may accelerate this so you know while its in the garage, rather than far from home.