I've had this before on quite a few connectors I've redone. Can't remember exactly what it is but it's not corrosion. I think it was used to aid the connection of a suspect connector pin? Hopefully someone who knows better than me will chime in with exactly what this substance is but the important thing is there no need to replace the whole wire. Just repin as you're doing with the rest of the wires. 
I have seen that stuff too and I think it is exactly what you said, a type of anti-corrosion and pro-conductivity fluid
