Cannot get clutch to release into gear

[Bucko]

The previous owner rebuilt/replaced the clutch, the gasket appears very new.  At first, bike rode like a dream, then clutch began slipping.

Assuming the clutch was installed properly and with the upgraded spring parts (as opposed to just replacing the fibre plates)..neither of those assumptions may be correct  .. but for the sake of discussion: assuming the problem is in the hydraulic circuit....air in the lines wold make disengaging the clutch problematic.  Slipping clutch would indicate pressure build up in the line which is a symptom of a plugged bypass or equalizing hole in the master cylinder (the smaller of the two holes in a master cylinder)

[99 drifter]

Hi, first time here.  I have a 99' drifter 1500 I bought used.  The previous owner rebuilt/replaced the clutch, the gasket appears very new.  At first, bike rode like a dream, then clutch began slipping.  I checked the main reservoir and it was very low and extremely dirty,  After cleaning and bleeding, the clutch would function but was extremely touchy.  Would jump into gear, just barely releasing the clutch handle.  Only an experienced rider could deal with it.  I replaced the slave unit with a used one, bled the system and now the bike will not leave neutral.  Clutch pressure seems adequate but will not go into gear.  Any ideas on how to solve?  It's a shaft drive (as most of you will know).

Many thanks in advance.
Tim