The switch lasted 30 years.The problem occur when the blower motor is asking to much current for some time because of bad bearing. The switch and wiring around it get overheated and finaly give up.Since you already adressed the problem of the blower, yo should be fine with a new switch.http://www.cbsonline.co.uk/3-speed-heater-fan-switch--swfan-1578-p.asp
Very nice job. I have to redo mine again, since the plastic broke and the motor fell and dragged the blower wheel inside the housing. A temporary fix with metal reinforcement should hold until I can come up with a better replacement.