In a similar position myself, here's a exploded view of the internal components:
I had to stretch out the plunger spring as it lost some of its original force and wasn't returning down.
Replace the internal seals also. They are cheap from simplybearings.co.uk, just standard shaft lip seals, sizes are 4x9x3 and 14x25x5
p.s. always take photos as you disassemble stuff, for this exact reason!