NAALOX grease instead of gold kit connector upgrade? Preventative?

Hi, I have an 87 Mondial and recently the aircon/heater fan stopped working. After many hours under the dash I (partly spent removing alarm systems no longer used) I narrowed it down to two fairly burnt looking connectors - the one on the end of the fuse/relay box and one in the passenger footwell - (specifically pin 1 and possibly pin 2 on connector C12 in fig 13 of the wiring manual). What I would like to know is whether or not the connections failed due to over current, in which case why didn't the fuse blow, or whether it was just contact resistance that caused enough heat to melt the plastic connector housing. The fact that it is two connectors in line would make me think it was over current but the fuse didn't blow.

The other question is what do people normally do about this sort of problem. Are the connectors easy to replace?

I'm not totally sure this is the correct thread but it seems related

 

This. When the current is 8~10~15A, the I^2*R heating is significant enough to do damage even if the resistance at the connection is only a few tens of milliOhms.