So far just about everything the old CT3 has in switches has needed cleaning or replacing. Wondering what the durability is on the rectifier? I can get a new one for under $20 and was wondering if I needed to keep one on hand or are they very durable?

Rectifier is a diode.  Can be tested fairly easy.  I've not known them to be unreliable but they can be damaged by even a split second of reversed battery connection or a bit of overload/short of battery + to ground with engine running. 

I have seen a few that seem to spontaneously melt down but always on someone else's bike so hard to say what may have happened.