Cabin heater-a/c fan no longer runs at low speed. Speeds 2-5 work fine

What is your question?

I've just lost the low heating-a/c fan speed in my old truck with only 62k miles. From what I've seen the problem most likely is a resistor plugged into the fan motor within a plastic enclosure beneath the dashboard. I can live without the low speed; however, it appears that after a while I'll have only the high speed. Dealer quote is in excess of $150 for this repair. I'm pretty handy and have a complete set of tools, but I'm not experienced at electrical diagnostics. Is this resistor something I should be able to replace myself? Is it available from sources other than GM dealers? Thanks for your help.