hi bud i have the same bike and same problem ,when i first bought my bike i noticed the clutch was spongy and did`nt clear right after taking it home i found it was low on fluid. the bike had been laid up for a few years so i bled the clutch and it was fine for a while then had to bleed it again then again all the time fluid was black soon after being bled .
on monday when out to oban whith the scottish ride oot lol my clutch gave up 2 miles from my house so i took the slave off and found it to be leaking theres 2 seals 1 the main seal that makes the clutch work and 2 second small seal to seal the clutch push-rod my guess is small seal is ****** causing the main seal to go as hot engine oil making the rubber soft when i looked inside the slave with the piston out there is no wear inside and piston is good with no marks so im going to replace the 2 seals and it should be fine ..
http://www.ultimateparts.net/aprili...00-2000-Aprilia-Spare-Parts-Genuine-&i=363189
looks like the small seal you can get on its own im sure thats no problem to me as
a gearbox builder i can get my hands on bearing and seals of any kind
will post my results as soon as its fixed