Could it be a faulty seal on the new clutch cylinder? Think it's called input seal?
I can't really see how it could be anything to do with the slave cylinder, that device is only connected to the hydraulic clutch fluid system (which is most probably a clear/yellow liquid). The slave cylinder is never in contact with the red gearbox oil.
If you are getting red transmission fluid coming out of the bottom of the F23 it must be leaking from inside the gear/cog compartment into the bell housing by the sounds of it.
If you can take the box off, and search for witness marks of the fluid, I suspect you will find a tiny crack somewhere, a quick spotweld on it might fix it, or possibly use some epoxy/liquid metal on it.
Good luck.