clutch pedal went soft

[DSM_brother2]

so now it is slipping like crazy in 4th and 5th. i kno my rear main is leaking alittle, could this be the problem? i got the tranny clutch and flywheel from iceminion, and ive put 1300 on the clutch, new tranny. it was a used clutch but looked good. how could this be fixed without pulling the tranny???