The stabilizer can be re-used.

Part C can be dark (more or less Purple) and even then it will work (the C41 developer) together with part A, part B and the starter.

Note: For the mini kit (0,5 ltr.) there is stabilizer for 250ml (total volume) so if you're using a 500ml or 600ml tank for roll film you have to rotate the tank carefully.

For practical use you can even use 270ml instead of 250ml for rotary (Jobo) development (so add 20ml extra water only) and use 2x2 films with the next times:
Pre-wash: 2 minutes
C41 developer: 3:15 minutes
Water change
Bleach: 4 minutes
Water change
Fix: 6 minutes
Wash the film: 3-5 minutes
Stabilizer: 1 minut

Dry the film(s).

The best way is a Jobo CPE/CPA or CPP processor with elevator. The stabilizer outside the processor due to foam which can contaminate the elevator system. In this way a C41 film development is really a piece of cake.